Polypropylene resin expanded particle and molded article using it

ABSTRACT

A specific relationship must be met in case of: (a) a structural unit derived from propylene is present in 100 to 85 mole %, and a structural unit derived from ethylene and/or alpha-olefin with 4 to 20 carbons is present in 0 to 15 mole %; (b) a content of a position irregularity unit based on 2,1-insertion of a propylene monomer unit in all propylene insertions, which is measured by 13C-NMR, is 0.5% to 2.0% and a content of a position irregularity unit based on 1,3-insertion of propylene monomer unit in all propylene insertions, which is measured by 13C-NMR, is 0.005% to 0.4%; and  
     (c) a water vapor transmission rate is Y [9/M 2 /24 hr] as film and a melting point Tm[° C.] shows specific relationship.

TECHNICAL FIELD

A first associated invention of the present application relates to apolypropylene based resin expanded particle having its significantlyuniform foam diameter and capable of obtaining a molded article with itssuperior surface appearance or the like, and a molded article using theparticle.

BACKGROUND ART

A molded article derived from a polypropylene based resin expandedparticle has its superior chemical resistance, shock resistance, andcompression strain recovery properties or the like as compared with amolded article derived from a polystyrene based resin expanded particle.Thus, this molded article is suitably used as a bumper core material forautomobiles or the like or a variety of packaging materials.

As the above polypropylene based resin, from an aspect of foamingcharacteristics, there is employed a propylene-alpha-olefin randomcopolymer obtained by primarily copolymerizing alpha-olefin such asethylene or 1-butene or the like with propylene. These are polymerizedby employing a so called Ziegler-Natta catalyst which consists oftitanium chloride and alkyl aluminum.

In recent years, there is provided a proposal in which polypropylenehaving a syndiotactic structure obtained by employing a so calledmetallocene based catalyst is employed for a substrate of a foamedarticle (JP 1992-224832 Unexamined Patent Publication (Kokai)). By thisproposal, it is possible to produce a foamed article with a propylenehomopolymer.

However, there has been a problem that polypropylene having asyndiotactic structure has a low melting point as compared withpolypropylene having an isotatic structure, and is inferior thereto inmechanical properties.

Further, in JP 1994-240041 Unexamined Patent Publication (Kokai) (PatentDocument 1), there is proposed a polypropylene based resin expandedparticle in which an isotactic polypropylene based resin polymerized byemploying a metallocene based polymer catalyst is obtained as a baseresin.

In this case, although the present invention is characterized in thatthe foam diameters of foam particles are comparatively uniform, theuniformity is not always sufficient, and further improvement has beendesired.

Therefore, the object of the first associated invention of the presentapplication is to provide a polypropylene based resin expanded particlecapable of obtaining a molded article with its significantly uniformfoam diameters, and having its superior surface appearance andmechanical properties; and a molded article thereof.

DISCLOSURE OF THE INVENTION

According to the first aspect of the first associated invention, thereis provided a polypropylene resin expanded particle characterized bycomprising a polypropylene based polymer having the followingrequirements (a) to (c) as a base resin:

(a) a structural unit derived from propylene is present in 100 to 85mole %, and a structural unit derived from ethylene and/or alpha-olefinwith 4 to 20 carbons is present in 0 to 15 mole %;

(b) a content of a position irregularity unit based on 2,1-insertion ofa propylene monomer unit in all propylene insertions, which is measuredby 13C-NMR, is 0.5% to 2.0% and a content of a position irregularityunit based on 1,3-insertion of propylene monomer unit in all propyleneinsertions, which is measured by 13C-NMR, is 0.005% to 0.4%; and

(c) in the case where a melting point is defined as Tm [° C.], and wherea water vapor transmission rate when made into a film is defined as Y[g/m²/24 hr], Tm and Y meet the following formula (1)(−0.20)·Tm+35≦Y≦(−0.33)·Tm+60   Formula (1).

In the present invention, a propylene based polymer having the aboverequirements (a) to (c) is provided as a base resin, and thus, there canbe provided a polypropylene based resin expanded particle having itssignificantly uniform foam diameter In addition, there can be provided apolypropylene based resin expanded particle capable of obtaining amolded article which is superior in mechanical properties such assurface appearance, compression strength, and tensile strength.

According to the second aspect of the present invention, there isprovided a molded article, made by molding polypropylene resin expandedparticles in a mold and having density of 0.5 g/cm³ to 0.008 g/cm³,wherein the polypropylene resin expanded particles are the ones claimedin any of claims 1 to 4. (claim 5)

In this case, as the above described polypropylene based resin expandedparticle, one claimed in any of claims 1 to 4 is employed and molded,and the molded article has the above density.

Therefore, the molded article is superior in surface appearance such assmoothness or gloss properties, and is superior in mechanical propertiessuch as compression strength or tensile strength.

If the density of the molded article is greater than 0.5 g/cm³, thepreferred characteristics of a foamed article such as light weightproperties, shock absorption properties, or heat resistance are notsufficiently provided, and there is a danger that cost efficiency islowered because of low foaming magnificence.

On the other hand, if the density is smaller than 0.008 g/cm³, there isa tendency that the closed cell ratio is lowered, and there is a dangerthat mechanical properties such as bending strength or compressionstrength are insufficient.

Therefore, the above molded article is suitable for a packages, a toy,automobile parts, a helmet, a core material, or a cushioning packagingmaterial and the like.

In the first aspect of the present invention (claim 1) a description ofrequirement (a) will be given firstly with respect to a polypropylenebased polymer employed as the above base resin.

The above described requirement (a) is a propylene homopolymer (100%) oran copolymer consisting of propylene with ethylene and/or alpha-olefinwith 4 to 20 carbons.

As for ethylene and/or alpha-olefin with 4 to 20 carbons as a comonomercopolymerized with the above propylene, there can be specificallyexemplified ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene,4-methyl-1-butene or the like.

The above polypropylene based polymer can be obtained by using a socalled metallocene based catalyst, for example.

In addition, in the present invention, a polypropylene based resinobtained by employing monomers in copolymerizing with propylene, whichhas been hardly polymerized by a conventional Ziegler-Natta catalyst,can be employed as a base resin for producing the expanded particle.

As these monomers, there can be exemplified one or two kinds of a cyclicolefin such as cyclopentene, norbornene,1,4,5,8-dimetano-1,2,3,4,4a,8,8a,5-octahydronaphtalene; non-conjugatediene such as 5-methyl-1,4-hexadiene, 7-methuyl-1, or 6-octadiene; andan aromatic unsaturated compound such as styrene or divinyl benzene.

The propylene based polymer for use in the present invention is apropylene based (co)polymer resin which contains 85 mole % to 100 mole %of a structural unit derived from propylene contained in the propylenebased polymer. In addition, it is required that the structural unitderived from ethylene and/or alpha-olefin with 4 to 20 carbons iscontained at a content of 0 mole % to 15 mole %.

In the case where the structural unit of comonomer is beyond the aboverange, the mechanical properties such as bending strength or tensilestrength of a base resin are greatly lowered, and a target expandedparticle and a molded article derived therefrom is not obtained.

Next, as shown in the above requirement (b), the above propylene basedmonomer is 0.5% to 2.0% at a content of a position irregularity unitbased on 2,1-insertion of a propylene monomer unit in all propyleneinsertions measured in 13C-NMR, and a content of a position irregularityunit based on 1,3-insertion of propylene monomer unit is 0.005% to 0.4%.

With respect to 0.5% to 2.0% of the former, there is a problem that anadvantageous effect of uniform foam diameter in the expanded particle issmall if the diameter is less than 0.5%, and there is a problem that, if2.0% is exceeded, the mechanical properties of the base resin, forexample, bending strength or tensile strength, is lowered. Thus, thereis a problem that the strength of particle strength and the moldedarticle derived therefrom are lowered.

In addition, with respect to 0.005% to 0.4% of the latter, there is aproblem that, if the content is less than 0.005%, an advantageous effectof uniform foam diameter in the expanded particle is small, and there isa problem that, if 0.4% is exceeded, the mechanical properties of thebase resin, for example, bending strength or tensile strength, islowered, and thus, there is a problem that the expanded particle and themolded article derived therefrom is lowered.

Here, the structural unit derived from propylene contained in apropylene based polymer and/or the fraction of the structural unitderived from alpha-olefin with 4 to 20 carbons, and the isotactic triadfraction descried later are values measured by employing a 13C-N Rtechnique.

A 13C-NMR spectrum measuring technique is as follows, for example. Thatis, a sample of 350 mg to 500 mg was put into an NMR sample tube of 10mm in diameter; a solvent was completely dissolved by employing amixture of about 0.5 ml of deuterated benzene for locking and about 2.0ml of o-dichlorobenzene; and then, measurement was carried out under aproton complete de-coupling condition at 130° C.

Under a measurement condition, a flip angle of 65 deg, a pulse intervalof 5T1 or more (provided if T1 is the longest value in a spin latticerelaxation time of a methyl group) was selected. In a propylene polymer,the spin lattice relaxation time of the methylene group and methinegroup is shorter than that of the methyl group, and thus, the recoveryof magnetization of all carbons is 99% or more under the measurementcondition.

Although the detection sensitivity of a position irregularity unit underthe 13C-NMR technique is generally about 0.01%, the sensitivity can beenhanced by increasing the scanning time.

In addition, a chemical shift in the above measurement is set asfollows. A peak of a methyl group of a third unit of 5 chains of apropylene head-to-tail unit which is identical in a direction of methylbranch was set at 21.8 ppm, and a chemical shift of another carbon peakwas set with this peak being a reference.

When this reference is employed, a peak based on a methyl group in asecond unit of three chains of the propylene unit indicated by PPP [mm]in the following formula [chemical formula 1] appears in the range of21.3 to 22.2 ppm; a peak based on a methyl group in a second unit of thethree chains of the propylene unit indicated by PPP [mr] appears in therange of 20.5 ppm to 21.3 ppm; and a peak based on a methyl group in asecond unit of the three chains of the propylene unit indicated by PPP[rr] appears in the range of 19.7 ppm to 20.5 ppm.

Here, PPP[mm], PPP[mr], and PPP[rr] are indicated respectively as shownbelow.

Further, the propylene polymer of the present invention contains aspecific amount of the following partial structures (I) and (II) whichincludes a position irregularity unit based on 2,1-insertion and1,3-insertion of propylene.

Such a partial structure is considered to be produced by the positionirregularity which takes place during polymerization of propylene in thecase where reaction has been carried out by employing a metallocenebased catalyst, for example.

That is, a propylene monomer, in general, reacts in a fashion in which amethylene carbon is bonded with a metal portion in a catalyst, i.e.,under “1,2-insertion”. Rarely, “2,1-insertion” or “1,3-insertion” maytake place. “2,1-insertion” is a reaction format in which an addingdirection is reversed from “1,2-insertion”, and a structural unitrepresented by the above partial structure (I) is formed in a polymerchain.

In addition, “1,3-insertion” means propylene monomers are taken in apolymer chain with their C-1 and C-3, and as a result, a straight chainshaped structural unit, i.e., the above partial structure (II) isgenerated.

The mm fraction in all the polymer chains of the propylene polymeraccording to the present invention is represented by the followingmathematical formula 1. It should be noted that in partial structure(II), as a result of 1,3-insertion, a methyl group derived from apropylene monomer disappears by one.${{mm}\quad(\%)} = {\frac{\begin{matrix}{{{area}\quad{of}\quad{methyl}\quad{group}\quad\left( {{\left. 21.1 \right.\sim 21.8}\quad{ppm}} \right)} - {3 \times}} \\\frac{\begin{pmatrix}{A < 1 > {+ A} < 2 > {+ A} < 3 > +} \\{A < 4 > {+ A} < 5 > {+ A} < 6 >}\end{pmatrix}}{6}\end{matrix}}{\begin{matrix}{{\Sigma\quad{ICH}_{3}} - {4 \times}} \\{\frac{\begin{pmatrix}{A < 1 > {+ A} < 2 > {+ A} < 3 > +} \\{A < 4 > {+ A} < 5 > {+ A} < 6 >}\end{pmatrix}}{6} -} \\\frac{\left( {A < 7 > {+ A} < 8 > {+ A} < 9 >} \right)}{3}\end{matrix}}.}$

In this formula, ΣICH₃ indicates an area of all methyl groups (all thepeaks of 19 ppm to 22 ppm of chemical shift). In addition, A<1>, A<2>,A<3>, A<4>, A<5>, A<6>, A<7>, A<8>, and A<9>are areas of peaks of 42.3ppm, 35.9 ppm, 38.6 ppm, 30.6 ppm, 36.0 ppm, 31.5 ppm, 31.0 ppm, 37.2ppm, and 27.4 ppm, respectively, and indicate contents of carbonsindicated by partial structures (I) and (II).

In addition, a rate of 2,1-inserted propylene with respect to all thepropylene insertions and a rate of 1,3-inserted propylene werecalculated in accordance with the following mathematical formula 2.$\begin{matrix}{{a\quad{content}\quad{of}\quad 2},{1 -}} \\{{inserted}\quad{propylene}\quad(\%)}\end{matrix} = {\frac{\begin{pmatrix}\begin{matrix}{A < 1 > {+ A} < 2 > +} \\{A < 3 > {+ A} < 4 > +}\end{matrix} \\{A < 5 > {+ A} < 6 >}\end{pmatrix}/6}{\begin{matrix}{{sum}\quad{of}\quad{integral}} \\{{value}\quad{of}\quad{\left. 27 \right.\sim 48}\quad{ppm}}\end{matrix}} \times 1000 \times \frac{1}{5}}$ $\begin{matrix}{{a\quad{content}\quad{of}\quad 1},{3 -}} \\{{inserted}\quad{propylene}\quad(\%)}\end{matrix} = {\frac{\begin{pmatrix}{A < 7 > {+ A} < 8 > +} \\{A < 9 >}\end{pmatrix}/6}{\begin{matrix}{{sum}\quad{of}\quad{integral}} \\{{value}\quad{of}\quad{\left. 27 \right.\sim 48}\quad{ppm}}\end{matrix}} \times 1000 \times \frac{1}{5}}$

Next, with respect to requirement (c), there is shown a relationshipbetween water vapor transmission rate and a melting point in the casewhere a propylene based polymer as a base resin is used as a film.

That is, according to the propylene polymer of the present invention, inthe case where a melting point of the polymer is Tm[° C.] and the watervapor transmission rate is Y [g/m²/24 hr] when the polymer is formedinto a film, Tm and Y meet the following relational formula (1).(−0.20)·Tm+35≦Y≦(−0.33)·Tm +60   Formula (1)

The above water vapor transmission rate can be measured by JIS K7129“Stream Transparency Testing Method of Plastic Film and Sheet”. In thecase where a value Y of water vapor transmission rate is in the aboverange, the size of foams in expanded particles become extremely uniform.

In the case where the value Y exceeds the value of formula (1) and inthe case where it is lower than the range of formula (1), thenon-uniformity of the diameters of foams in expanded particlesincreases. As a result, there can only be obtained an expanded particlewith inferior which mechanical properties when molding is effected in amolded article.

Although this reason is not clear, it is presumed that a balance betweenimpregnation and escape of a blowing agent is associated when anexpanded particle is produced by discharging it in a low pressureatmosphere; and this balance becomes preferable in the case where apropylene based polymer is employed such that the melting point (Tm) andwater vapor transmission rate (Y) meets a relationship of formula (1).

The polypropylene based expanded particle according to the presentinvention is employed as a material for obtaining a molded article byfilling the particle in a mold, heating the filled particle, and foamingit.

Next, it is preferable that the above polypropylene based polymerfurther has the following requirement (d) (claim 2):

(d) An isotactic triad fraction of a propylene unit chain part whichconsists of a head-to-tail linkage measured by 13C-NMR is 97% or more.

In this case, there can be attained an advantageous effect that theuniformity of the size of foams contained in the expanded particles isfurther improved.

That is, apart from the above described requirements (a) to (c), apropylene based polymer as the above base resin is employed the onewhose isotactic triad fraction (i.e., a rate of three propylene unit inwhich propylene units are bonded with each other in a head-to-tailmanner and the direction of methyl branch in the propylene unit isidentical, out of the arbitrary three propylene unit in the polymerchains) measured by 13C-NMR (nuclear magnetic resonance technique), is97% or more.

Hereinafter, the isotactic triad fraction is described as an mmfraction. In the case where the mm fraction is less than 97%, there is adanger that the mechanical properties of a base resin are lowered, andthe mechanical properties of a molded article consisting of a expandedresin particle derived by using this resin are lowered as well.

Further preferably, the mm fraction is 98% or more.

It is preferable that the above propylene based polymer further has thefollowing requirement (e) (claim 3):

(e) a melt flow rate is 0.5 g/10 minutes to 100 g/10 minutes.

In this case, there can be attained an advantageous effect that theexpanded particles can be produced while they maintain productivitywhich is useful in commercial production, and the physical properties ofa molded article consisting of the derived foam particles are excellent.

If the above melt flow rate (MFR) is less than 0.5 g/10 minutes, thereis a danger that the productivity of expanded particles, in particular,productivity under the melting and kneading process described later islowered. In addition, in the case where the MFR exceeds 100 g/10 minutesdescribed above, there is a danger that dynamic properties such ascompression strength and tensile strength of a molding element derivedby employing the foam particles obtained as a product are lowered.Preferably, the melt flow rate is 1.0 g/10 minutes to 50 g/10 minutes,and is further 1.0 g/10 minutes to 30 g/10 minutes.

Next, it is preferable that the above polypropylene resin expandedparticle contains a blowing agent which meets the following requirement(f) (claim 4):

(f) in the case where a critical temperature of the blowing agent isdefined as Tc [° C.], Tc meets the following formula (2)−90≦Tc≦400   Formula (2).

In this case, there is a tendency that the foam diameters of theobtained expanded particles are uniform. As a result, the dynamicproperties of a molded article obtained by employing such foam particlesare improved. If Tc is lower than −90° C., the non-uniformity of thefoam diameters of the obtained foam particles becomes significant.Although this reason is not clear it is estimated that low Tc results insudden foaming.

On the other hand, if Tc is higher than 400° C., there is a danger thatit is very difficult to obtain an expanded particle of 0.1 g/cm³ or lessin density, for example.

Specific example of the above blowing agents are as follows. A substancename is followed by critical temperature for each substance (° C.).There are exemplified: straight-chain or cyclic aliphatic hydrocarbonsor analogues such as methane (−82); ethane (32); propane (97); butane(152); isobutane (135); pentane (197); hexane (235); cyclopentane (239);or cyclohexane (280); halogenated hydrocarbons such asdichlorodifluoromethane (112) trichloromonofluoromethane (198); andinorganic gas such as carbon dioxide (31).

In addition, among from the blowing agent which meets the followingformula (2), in the case where the following formula (3) is met, thereis an advantage that special facilities or equipment are not requiredespecially when these blowing agents are handled.0≦Tc≦300   Formula (3)

Further, in the case where the following formula (4) is met, there is anadvantageous effect that, apart from the engineering effectivenessdescribed previously, the foam diameters of the expanded particlesobtained are very uniform.30≦Tc≦200   Formula (4)

The above blowing agent may be used alone, or in combination of the twoor more.

In addition, another polymer component or additive can be mixed with theabove described propylene based polymer (base resin) without departingfrom the advantageous effect of the present invention.

The other polymer components described above include: for example, anethylene based resin such as linear low density polyethylene which is acopolymer of ethylene and alpha-olefin (4 or more carbons), high densitypolyethylene, and low density polyethylene; a polybutene resin; anethylene-propylene based rubber; an ethylene-propylene-diene basedrubber; a styrene based thermoplastic elastomer such as a hydrogenatedblock copolymer obtained by saturating at least part of an ethylenicbased double bond of styrene-diene block copolymer, or styrene-dieneblock copolymer; and a modified polymer of these resin, elastomer, orrubber, by grafting of acrylic acid type monomer. In the presentinvention, these resins, elastomer, rubber or a modified polymer thereofcan be used independently or two or more thereof can be used incombination.

As the above described additives, a variety of additives such as anucleating agent, a coloring agent, an antistatic agent; a lubricatingagent can be added. These additives are usually added altogether duringmelting and kneading described later, and are contained in resinparticles.

The above nucleating agents includes organic nucleating agents such ascarbon, phosphate based nucleating agent, phenol based nucleus agent, oramine based nucleus agent as well as inorganic compounds such as talc,calcium carbonate, silica, titanium oxide, gypsum, zeolite, borax, oraluminum hydroxide. The amount of a variety of these additives is 15 wt.% or less with respect to 100 wt. % of a base resin of the presentinvention, is preferably 8 wt. % or less, and further preferably 5 wt. %or less, which is different depending on its purpose of addition.

Although mixing of the above other component to the base resin can becarried out where the polypropylene base resin is in a fluid state orsolid state, in general, melting and kneading is used. That is, forexample, the above base resin and the other components or the like arekneaded at a desired temperature by using a variety of kneading machinessuch as a roll, a screw, a Banbury mixer, a kneader; a blender; or amill. After kneading, the product is granulated into an appropriate sizeof particles suitable to production of expanded particles.

In addition, it is preferable to employ a method in which, after meltingand kneading has been carried out in an extruder, a kneading substanceis extruded in a standard from a die having small holes at a tip end ofthe extruder, and is cut in a predetermined weight or size by a cutterprovided with a pulling machine, thereby obtaining a resin particle.

In general, expanded particles can be produced smoothly without aproblem when the weight of one resin particle is from 0.1 mg to 20 mg.If the weight of one resin particle is in the range of 0.2 mg to 10 mgand if a deviation in weight between particles is small, the expandedparticles are easily produced. Then, the density distribution ofexpanded particles obtained is small, and the filling properties of theexpanded resin particles into the mold or the like are improved.

As a method for obtaining expanded particles, there can be used a methodfor performing heating and foaming after a volatile blowing agent hasbeen impregnated in resin particles; more specifically, any of themethods described in JP 1974-2183 Examined Patent Publication (Kokoku);JP 1981-1344 Examined Patent Publication (Kokoku); DE 1285722 UnexaminedPatent Publication (Kokai) ; and DE2107683 Unexamined Patent Publication(Kokai); or the like.

After the blowing agent has been impregnated in resin particles, in thecase where heating and foaming are carried out, resin particles are putinto a pressure vessel which can be closed and released, together with avolatile blowing agent; heating is carried out at or above the softeningtemperature of the base resin, and the volatile blowing agent isimpregnated in the resin particles. Then, after the contents within thevessel are discharged from the sealed container into a low pressureatmosphere, and drying is carried out. In this manner, expandedparticles are obtained.

It is preferable that the polypropylene based resin expanded particlesof the present invention have two or more endothermic peaks in a DSCcurve obtained by means of differential scanning calorimetry (the DSCcurve obtained when 2 mg to 4 mg of expanded particles are heated from20° C. to 200° C. at a rate of 10° C. by means of differential scanningcalorimeter). This phenomenon arises when a part derived from the abovebase resin forms an inherent endothermic peak and an endothermic peak ata higher temperature than the former.

The expanded particles of which two or more endothermic peaks appear onthe DSC curve are obtained by controlling a condition when the aboveresin particles are foamed, more specifically, by controlling thetemperature, the pressure, or a time and the like when discharging iscarried out into a low pressure atmosphere.

In a method for producing expanded particles by discharging the contentsof vessel into a low pressure atmosphere when a decomposition typeblowing agent is kneaded in advance in resin particles, it is possibleto obtain the above expanded particles even if no blowing agent is addedin to a pressure vessel.

As the above mentioned decomposition type blowing agent, any agent canbe used as long as it is decomposed at a foaming temperature of resinparticles and generates a gas. Specifically, sodium bicarbonate,ammonium carbonate, an azide compound, an azo compound and the like canbe exemplified.

In addition, during heating or foaming, it is preferable that water oralcohol and the like is used as a dispersion medium for resin particles.Further, it is preferable to use independently or in combination of twoor more: sparingly water soluble inorganic substance such as aluminumoxide, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, orkaolin; water soluble polymeric protective colloid such as polyvinylpyrrolidone, polyvinyl alcohol, or methyl cellulose; and anionic surfaceactive agent such as sodium dodecyl benzene sulfonate, or sodium alkanesulfonate so that resin particles are uniformly dispersed in adispersion medium.

When resin particles are discharged into a low pressure atmosphere, itis preferable to maintain the pressure in the vessel to be constant byintroducing inorganic gas or volatile blowing agent similar to the abovefrom the outside in order to facilitate the discharging of the beads.

Next the polypropylene based resin foam particles of the presentinvention are molded by using a mold under various conditions. Forexample, after the polypropylene based resin expanded particles havebeen filled into a mold cavity which consists of a pair of protrusiveand recessed molds at an atmospheric pressure or under pressurereduction, the cavity is compressed so that the volume is reduced by 5%to 70%. After that a hot medium such as steam is introduced into thecavity so as to heat and fuse the polypropylene based resin expandedparticles (for example, JP1971-38359 Examined Patent Publication(Kokoku)).

In addition, there is a pressure aging method in which the resinparticles are first treated with a volatile blowing agent or one or moreinorganic gases to enhance a secondary expanding force of the resinparticles; then filling the foam resin particles into a mold cavity atan atmospheric pressure or under reduced pressure while maintaining thesecondary foaming force; and then, introducing a hot medium into themold cavity to heat and fuse the expanded resin particles (for example,JP 1976-22951 Examined Patent Publication (Kokoku)).

In addition, there is a compression filling technique in which the moldcavity pressurized at an atmospheric pressure or higher by a compressivegas filled with the expanded particles which have been pressurized at orabove the pressure of the cavity, followed by introducing a hot mediumsuch as steam into the cavity to heat and fuse the expanded resinparticles (for example, JP 1992-46217 Examined Patent Publication(Kokoku)).

Further, there is a normal pressure filling technique for fillingexpanded resin particles into a cavity which consists of a pair ofprotrusive and recessed metal die at an atmospheric pressure or underreduced pressure by using the expanded particles with high secondaryexpanded force obtained under a specific conditions, followed byintroducing a hot medium such as steam into the cavity to heat and fusethe foam resin particles (for example, refer to JP 1994-49795 ExaminedPatent Publication (Kokoku)). Furthermore, molding can be performed by acombination of the above methods (for example, refer to JP 1994-22919Examined Patent Publication (Kokoku)).

Furthermore, a film can be laminated on the above foam molded article asrequired. The film to be laminated is not limited in particular, and,for example, there is employed: a polystyrene film such as OPS(bi-axially oriented polystyrene sheet), heat resistant OPS, or HIPS; apolypropylene film such as CPP (a non-oriented polypropylene film), OPP(a bi-axially oriented polypropylene film) or a polyethylene film; or apolyester film and the like.

Moreover, although there is no limitation to thickness of a film to belaminated, in general, a film having a thickness of 15 micron to 150micron is employed. Printing may be applied on these films as required.In addition, lamination may be carried out at the same time whenexpanded particles are molded to be heated and fused. Further,lamination may be carried out on molded element. Lamination can also becarried out by employing a hot melt adhesive as required.

The description of the first associated invention has now beencompleted.

SECOND ASSOCIATED INVENTION

Now, the second associated invention will be described here.

The second associated invention of the present application relates to apolypropylene resin expanded particle which has significantly uniformfoam diameter, which exhibits excellent fusion properties, which iscapable of lowering a molding temperature for obtaining a moldedarticle, and moreover, which is capable of producing an molded articlehaving an excellent surface appearance or the like, and a molded articleusing the particle.

A resin expanded particle has a low thermal conductivity owing to itsclosed cell structure. Thus, this particle is widely used as rawmaterial in obtaining molded articles such as heat insulation materials,cushioning materials, or various core materials. In addition, as athermoplastic resin constituting the above resin expanded particle, ingeneral, there are used polyethylene, polypropylene, polystyrene or thelike.

Among the above described thermoplastic resins, there is an advantagethat an expanded molded article obtained by using a resin expandedparticle obtained by using a resin having crystalline properties, i.e.,polyethylene or polypropylene is excellent in chemical resistance orheat resistance, as compared with a molded article obtained by using apolystyrene resin expanded particle.

However, in the case of a high melting point resin represented by apolypropylene resin, since a melting point is as high as 135° C. orabove, a high pressure steam exceeding 0.2 MPaG (hereinafter, referredto as G: Gauge pressure) is required as a pressure for fusing the resinexpanded particles during molding in a mold.

Thus, there is a disadvantage that the molding cost increases, andmoreover, a molding cycle is extended. In addition, in the case of theresin expanded particle made of the above described high melting pointresin, molding cannot be performed in a molding machine for expandablepolystyrene. Thus, a molding machine that has a high pressure steamcontrol system and a high mold closing pressure is required.

On the other hand, in the case of a polyethylene resin, since a meltingpoint is as low as 125° C. or below, it is sufficient if the steampressure for fusing the resin expanded particles has a low pressure ofless than 0.2 MPaG. Thus, there is provided an advantage that moldingcan be performed even by a molding machine for expandable polystyrenewith almost no change of specification.

However, an expanded molded article of a polyethylenic resin is low inheat resistance, since a base resin has a low melting point.Particularly, for a molded article having high expansion ratio, energyabsorption performance is small. Therefore, the expanded molded articleof the polyethylene resin can be generally used only at low expansionratio, as compared with another expanded molded articles of otherthermoplastic resins.

In order to solve various problems as described above, in JP 1998-77359Unexamined Patent Publication (Kokai), there is proposed a resinexpanded particle having a specific structure, the resin expandedparticle comprising a core layer in an expanded state comprising acrystalline thermoplastic resin and a coat layer comprising an ethylenepolymer which is substantially in a non-expanded state.

In this case, a resin expanded particle exhibiting excellent fusionproperties can be obtained even when the heated steam pressure inmolding is low. However, the mechanical strength of a molded articleobtained is not sufficient, and further improvement has been desired.

Patent Document 2

-   JP 1998-77359 Unexamined Patent Publication (Kokai) (pages 2 to 4)

Therefore the object of the second associated invention of the presentinvention is to provide a polypropylene resin expanded particle whichhas significantly uniform foam diameters and which is capable ofobtaining, even if molding is performed with a general-purpose moldingmachine with a low mold closing pressure, a molded article excellent insurface appearance, mechanical properties, fusion between expandedparticles, and in heat resistance; and a molded article thereof.

The first aspect of the second associated invention is a polypropyleneresin expanded particle characterized by comprising:

a core layer in an expanded state comprising of a crystallinethermoplastic resin; and

a coat layer comprising of a thermoplastic resin covering the above corelayer,

wherein the above core layer is a propylene polymer having the followingrequirements (a) to (c):

(a) a structural unit derived from propylene is present in 100 to 85mole %, and a structural unit derived from ethylene and/or alpha-olefinwith 4 to 20 carbons is present in 0 to 15 mole %;

(b) a content of a position irregularity unit based on 2,1-insertion ofa propylene monomer unit in all propylene insertions, which is measuredby 13C-NMR, is 0.5% to 2.0%, and a content of a position irregularityunit based on 1,3-insertion of propylene monomer unit in all propyleneinsertions, which is measured by 13C-NMR, is 0.005% to 0.4%; and

(c) in the case where a melting point is defined as Tm [° C.], and wherea water vapor transmission rate when made into a film is defined as Y[g/M²/24 hr], Tm and Y meet the following formula (1)(−0.20)·Tm+35≦Y≦(−0.33)·Tm+60   Formula (1). (claim 6)

The above resin expanded particle of the first invention of the secondassociated invention is comprised of: a core layer comprising thepropylene polymer having the above described requirements (a) to (c) asa base resin; and a coat layer coating the core layer.

Therefore, the above resin expanded particle can exhibit significantlyuniform foam diameters and is capable of obtaining, even if molding isperformed with a general-purpose molding machine with a low mold closingpressure, a molded article excellent in surface appearance, mechanicalproperties, and fusion between expanded particles, and in heatresistance.

The second aspect of the second associated invention is a molded, madeby molding polypropylene resin expanded particles in a mold and havingdensity of 0.5 g/cm³ to 0.008 g/cm³, wherein the above polypropyleneresin expanded particles are the one which is described in the abovefirst invention of the second associated invention (claim 6). (claim 12)

In this case, as the above described polypropylene resin expandedparticle, that of the first invention of the second associated inventionis used, and thus, a molded article has the above density.

Therefore, the molded article is excellent in surface appearance such assmoothness or glossiness, and is excellent in mechanical properties suchas compression strength or tensile strength.

If the density of the molded article is greater than 0.5 g/cm³, there isa possibility that preferred characteristics of an expanded article suchas weight reduction, shock absorption properties or heat resistance arenot sufficiently provided, and cost efficiency is lowered because of alow expansion ratio.

On the other hand, if the density is smaller than 0.008g/cm³, there is apossibility that the closed cell ratio is prone to decrease, andmechanical properties such as bending strength and compression strengthor the like are insufficient.

Therefore, the above described molded article is suitable for, forexample, packages, toys, automobile parts, helmet core materials, andcushioning packaging materials or the like.

The polypropylene resin expanded particle of the second associatedinvention has a complex structure formed of a core layer and a coatlayer.

In the first invention of the second associated invention (claim 6),first, requirement (a) will be described with respect to a propylenepolymer for a base resin of the above core layer is provided.

The base resin used here means a substrate resin component constitutingthe core layer. The core layer is made of the above base resin, otherpolymer components which is added according to need, and additives suchas catalyst neutralizing agent, lubricating agent, nucleating agent, andany other resin additive.

The above described requirement (a) is a propylene homopolymer (100%) ora copolymer of propylene and ethylene and/or alpha-olefin of 4 to 20carbons.

As ethylene and/or alpha-olefin with 4 to 20 carbons, of comonomers,which are copolymerized with propylene, there can be specificallyexemplified: ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or4-methyl-1-butene and the like.

The above polypropylene polymer can be obtained by using a so-calledmetallocene catalyst, for example.

In addition, in the first invention of the second associated invention,a polypropylene based resin obtained by employing monomers which hasbeen hardly polymerized by a conventional Ziegler-Natta catalyst, incopolymerizing with propylene, can be employed as a base resin forproducing an expanded particle.

As these monomers, there can be exemplified one or more kinds of cyclicolefin such as cyclopentene, norbornene,1,4,5,8-dimethano-1,2,3,4,4a,8,8a,5-octahydronaphthalene; non-conjugatediene such as 5-methyl-1,4-hexadiene, 7-methyl-1,6-octadiene; and anaromatic unsaturated compound such as styrene or divinylbenzene.

The propylene polymer for use in the first invention of the secondassociated invention is a propylene based (co)polymer resin whichcontains 85 mol % to 100 mol % of the structural unit derivedfrompropylene contained in the propylene polymer. In addition, it isrequired that the structural unit derived from ethylene and/oralpha-olefin with 4 to 20 carbons is contained at a content of 0 mol %to 15 mol %.

In the case where the structural unit of a comonomer is beyond the aboverange, the mechanical properties such as bending strength or tensilestrength of the core layer are greatly lowered, and the target expandedparticle and a molded article derived therefrom cannot be obtained.

Next, as shown in the above requirement (b), the above propylene polymerhas 0.5% to 2.0% at a content of a position irregularity unit based on2,1-insertion of a propylene monomer unit in all propylene insertionsmeasured by 13C-NMR, and a content of position irregularity unit basedon 1,3-insertion of propylene monomer unit is 0.005% to 0.4%.

With respect to 0.5% to 2.0% of the former, there is a problem that theadvantageous effect of uniform foam diameter in expanded particles issmall if the content is less than 0.5%, and there is a problem that if2.0% is exceeded, the mechanical properties of the base resin, forexample, bending strength or tensile strength, is lowered. Thus, thereis a problem that the strength of expanded particles and the moldedarticle derived therefrom are lowered.

In addition, with respect to 0.005% to 0.4% of the latter, there is aproblem that if the content is less than 0.005%, an advantageous effectof uniform foam diameter in the expanded particles is small, and thereis a problem that, if 0.4% is exceeded, the mechanical properties of thebase resin, for example, bending strength or tensile strength, islowered, and thus, there is a problem that the expanded particles andthe molded article derived therefrom is lowered.

Here, the contents of the structural unit derived from propylene in thepropylene polymer, the content of the structural unit derived fromethylene and/or alpha-olefin with 4 to 20 carbons in the above propylenepolymer, and the isotactic triad fraction described later are measuredby employing a 13C-NMR technique.

For the 13C-NMR spectrum measurement technique, refer to the above firstassociated invention.

Further, the propylene polymer of the second associated inventioncontains a specific amount of the above chemical formula 2 partialstructures (I) and (II) which includes a position irregularity unitbased on 2,1-insertion of propylene and 1,3-insertion. (refer to thefirst associated invention).

The mm fraction in all polymer chains of the propylene polymer accordingto the second associated invention is expressed by the abovemathematical formula 1 (refer to the first associated invention).

The mm fraction in all polymer chains of the propylene polymer accordingto the first invention of the second associated invention is representedby the following mathematical formula 1. It should be noted that inpartial structure (II), as a result of 1,3-insertion, a methyl groupderived from a propylene monomer disappears by one.

In addition, a content of 2,1-inserted propylene and a content of1,3-inserted propylene with respect to all propylene insertions arecalculated by the above mathematical formula 2 (refer to the firstassociated invention).

Next, with respect to requirement (c), a relationship between watervapor transmission rate and a melting point in the case where apropylene polymer as a base resin has been made into a film is shown.

That is, according to the propylene polymer in the first invention ofthe second associated invention, in the case where a melting point ofthe polymer is defined as Tm [° C.] and the water vapor transmissionrate when the polymer is molded into a film is defined as Y [g/m²/24hr], Tm and Y satisfy the following relational formula (1).(−0.20)·Tm+35≦Y≦(−0.33)·Tm+60   Formula (1)

The above water vapor transmission rate can be measured in accordancewith JIS K7129 “Testing methods for Water Vapor Transmission Rate ofPlastic Film and Sheeting”. In the case where a value Y of water vaportransmission rate is within the above range, the foam diameter inexpanded particles is extremely uniform.

In the case where the value Y exceeds a range of formula (1) and in thecase where it is lower than the range of formula (1), the non-uniformityof size of foams in expanded particles increases. As a result, there canbe only be obtained an expanded particle with inferior mechanicalproperties when molding is effected in a molded article.

Although this reason is not clear, it is presumed that a balance betweenimpregnation and escape of a blowing agent is associated when anexpanded particle is produced by discharging it in a low pressureatmosphere; and this balance becomes preferable in the case where apropylene polymer is employed such that the melting point (Tm) and watervapor transmission rate (Y) meets a relationship of formula (1).

Next, it is preferable that a thermoplastic resin forming a coat layerin the first invention of the second associated invention be made of apolyolefin based resin or a polystyrene based resin. In this case,advantageous effect in which physical properties of the molded articleare excellent can be obtained. As a polyolefin resin, it is particularlypreferable that homopolymer of ethylene or propylene be used orcopolymer of them be used.

In addition, it is preferable that the coat layer be in a non-expandedstate or be substantially in a non-expanded state. In this case, therecan be attained advantageous effect that a molded article with excellentfusion between expanded particles is obtained.

The polypropylene resin expanded particle according to the firstinvention of the second associated invention is foamed and hot-fused bycharging it in a mold and heating, and is used as a material forobtaining a molded article.

Next, it is preferable that the above coat layer be characterized inthat the above coat layer comprises of an olefin polymer in which amelting point is lower than that of a thermoplastic resin forming theabove core, or an olefin polymer which shows substantially no meltingpoint (claim 7). In this case, there is advantageous effect that amolded article can be obtained at a lower temperature.

As an olefin polymer with a lower melting point than a thermoplasticresin for the core layer, there can be exemplified: high pressure lowdensity polyethylene, linear low density polyethylene, linear very lowdensity polyethylene; copolymer of ethylene with vinyl acetate,unsaturated carboxylic acids or unsaturated carboxylic acid esters, andthe like; or a propylene copolymer with ethylene or alpha-olefin oranalogous.

In addition, as the above olefin polymer which shows substantially nomelting point, for example, there can be exemplified a rubber orelastomer such as an ethylene-propylene rubber, anethylene-propylene-diene rubber, an ethylene-acrylic rubber; chlorinatedpolyethylene rubber; chlorosulfonated polyethylene rubber, and the like.These rubbers or elastomer can be used alone or in combination of thetwo or more.

Next, it is preferable that the above propylene polymer characterized inthat a propylene polymer of a core layer further has the followingrequirement (d) (claim 8):

(d) an isotactic triad fraction at a propylene unit chain part which hasa head-to-tail linkage, which is measured by 13C-NMR, is 97% or more.

In this case, there can be obtained advantageous effect that theuniformity of the size of foams in the expanded particles is furtherimproved.

That is, as the propylene polymer of the base resin for the above corelayer, there is used propylene polymer in which the isotactic triadfraction (that is, a rate of three propylene unit in which propyleneunits are bonded with each other in a head-to-tail manner, of arbitrarythree propylene unit in the polymer chains, and the direction of methylbranch in the propylene unit is identical) measured by 13C-NMR (nuclearmagnetic resonance technique), is 97% or more in addition to the alreadydescribed requirements (a) to (c).

Hereinafter, the isotactic triad fraction is described as an mmfraction. In the case where the mm fraction is less than 97%, there is adanger that the mechanical properties of the base resin is lowered, andthe mechanical properties of a molded article composed of resin expandedparticles derived by using this resin are lowered as well.

Further preferably, the mm fraction is 98% or more.

Next, it is preferable that the propylene polymer for the core layercharacterized in that a propylene polymer of the above core layerfurther has the following requirement (e) (claim 9):

(e) a melt flow rate is 0.5 g/10 minutes to 100 g/10 minutes.

In this case, there can be obtained advantageous effect that expandedparticles can be produced while maintaining productivity which is usefulin commercial production, and dynamic properties of a molded articlecomposed of the obtained expanded particles are excellent.

If the above melt flow rate (MFR) is less than 0.5 g/10 minutes, thereis a danger that the productivity of the expanded particles under themelting and kneading process described later is lowered. In addition, inthe case where the MFR exceeds 100 g/10 minutes descried above, there isa danger that dynamic properties such as compression strength or tensilestrength of a molded article derived by employing the expanded particlesobtained as a product are lowered. Preferably, the melt flow rate is 1.0g/10 minutes to 50 g/10 minutes, and is further 1.0 g/10 minutes to 30g/10 minutes Next, it is preferable that the above coat layer becharacterized in that the above coat layer is a composition in which aresin identical to a core layer is blended by 1 part by weight to 100parts by weight per 100 parts by weight of an olefin polymer (claim 10).

According to such a composition, the adhesion properties of the corelayer and coat layer is improved As a result, strong fusion amongexpanded particles in a molded article can be obtained by using theabove polypropylene resin expanded particles. As a result, the strengthor the like of the molded article is improved.

In the case of blending less than 1 part by weight, there is apossibility that advantageous effect of improving the degree of fusionamong expanded particles become insufficient. On the other hand, if the100 parts by weight described above is exceeded, there is a possibilitythat the steam pressure required for molding becomes higher. Furtherpreferably, the above rate is 2 parts by weight to 50 parts by weight.Furthermore preferably, the rate is 3 parts by weight to 10 parts byweight.

Next, it is preferable that the above polypropylene resin expandedparticles characterized in that the above polypropylene resin expandedparticle is foamed by using a blowing agent which meets the followingrequirement (f) (claim 11). (f) in the case where a critical temperatureof the above blowing agent is defined as Tc [° C.], Tc meets thefollowing formula (2):−90° C.≦Tc≦400° C.   Formula (2)

In this case, there is a tendency that the foam diameters of expandedparticles are uniform. As a result, the dynamic properties of a moldedarticle obtained by employing such expanded particles are improved. IfTc is lower than −90° C., the non-uniformity of foam diameters of theexpanded particles becomes significant. Although the reason is notclear, it is estimated that low Tc results in sudden foaming.

On the other hand, if Tc is higher than 400° C., there is a danger thatit is very difficult to obtain an expanded particle of 0.1 g/cm³ or lessin density, for example.

For a specific example of the above blowing agent, refer to the firstassociated invention.

In addition, among from the blowing agent which meets the above formula(2), in the case where the following formula (3) is met, there is anadvantage that special facilities or equipment are not requiredespecially when these blowing agents are handled.0° C.≦Tc≦300° C.   Formula (3)

Further, in the case where the following formula (4) is met, there isadvantageous effect that, apart from the engineering effectivenessdescribed previously, the foam diameters of the expanded particlesobtained are very uniform30° C.≦Tc≦200° C.   Formula (4)

The above blowing agent may be used alone or in combination of the twoor more.

In addition, other polymer components or additives can be mixed with theabove propylene polymer as the base resin according to the secondassociated invention within the range in which advantageous effect ofthe second associated invention is not degraded.

Although mixture of the other component with a propylene polymer as abase resin can be carried out where the polypropylene base resin is in afluid state or solid state, in general, melting and kneading is used.That is, for example, the above base resins and the other components orthe like are kneaded at a desired temperature by using variety ofkneading machines such as a roll, a screw, a Banbury mixer, a kneader, ablender, or a mill and the like. After kneading, the product isgranulated into an appropriate size of particles suitable to productionof expanded particles.

A raw material for polypropylene resin expanded particles according tothe first invention of the second associated invention is a compositeparticle which comprises of a core layer and a coat layer.

As such a specific production method for composite particles, forexample, the following methods can be used.

For example, there can be used a sheath-core shaped composite diedescribed in: JP 1966-16125 Examined Patent Publication (Kokoku); JP1968-23858 Examined Patent Publication (Kokoku); JP 1969-29522 ExaminedPatent Publication (Kokoku); and JP 1985-185816 Unexamined PatentPublication (Kokai) or the like.

In this case, two extruders are used. A thermoplastic resin constitutinga core layer is melted and kneaded by one extruder; a resin constitutinga coat layer is melted and kneaded by the other extruder; and then, asheath-core shaped composite composed of a core layer and a coat layeris discharged out from the die in a strand shape.

It is preferable to use a method for cutting the composite to aspecified weight or size by a strand cutter to obtain columnar pelletshaped resin particles comprising of the core layer and the coat layer.

In general, if the weight of one resin particle is 0.1 mg to 20 mg,there is no problem with production of expanded particles obtained byheating and foaming them. When the weight of one resin particle iswithin the range of 0.2 mg to 10 mg, if a deviation in weight betweenparticles is small, the expanded particles are easily produced, adeviation in density of expanded particles obtained is small, and thefilling properties of resin expanded particles into the mold or the likeare improved.

As methods for obtaining expanded particles from the above resinparticles, there can be used a method of performing heating and foamingafter a volatile blowing agent in the resin particles fabricated asdescribed above has been impregnated in the resin particles; morespecifically, any of the methods described in JP 1974-2183 ExaminedPatent Publication (Kokoku), JP 1981-1344 Examined Patent Publication(Kokoku), DE 1285722 Unexamined Patent Publication (Kokai), and DE2107683 Unexamined Patent Publication (Kokai) or the like.

After a blowing agent has been impregnated in resin particles comprisingof a core layer and a coat layer, in the case where heating and foamingare carried out, resin particles are put into a pressure vessel whichcan be closed or released, together with a volatile blowing agent;heating is carried out at or above the softening temperature of the corelayer contained in a base resin, and the volatile blowing agent isimpregnated in the resin particles.

Then, after the contents within the vessel are discharged from theclosed vessel into a low pressure, and drying is carried out. In thismanner, polypropylene resin expanded particles can be obtained.

It is preferable that a propylene polymer forming a core layer ofpolypropylene resin expanded particles of the first invention of thesecond associated invention have two or more endothermic peaks in a DSCcurve obtained by means of differential scanning calorimeter (the DSCcurve is obtained when 2 mg to 4 mg of expanded particles are heatedfrom 20° C. to 200° C. at a rate of 10° C. by means of differentialscanning calorimeter). This phenomenon arises when a part derived fromthe above base resin forms an inherent endothermic peak and anendothermic peak at a higher temperature than the former.

The expanded particles of which two or more endothermic peaks appear onthe above DSC curve are obtained by controlling the condition when theabove resin particles are foamed, more specifically, by controlling thetemperature, the pressure, and a time and the like when discharging iscarried out into a low pressure atmosphere.

In a method of producing expanded particles by discharging the contentsof the vessel into a low pressure atmosphere, when a decomposition typeblowing agent is kneaded in advance in resin particles comprising of thecore layer and coat layer, the blowing agent is added into the pressurevessel, it is possible to obtain the above expanded particles even if noblowing agent is added into a pressure vessel.

As the above mentioned decomposition type blowing agent, any agent canbe used as long as it is decomposed at a foaming temperature of resinparticles and generates a gas. Specifically, for example, sodiumbicarbonate, ammonium carbonate, an azide compound, and an azo compoundand the like can be exemplified.

In addition, during heating and foaming, it is preferable that water oralcohol and the like is used as a dispersion medium of resin particles(refer to the first associated invention)

When resin particles are discharged into a low pressure atmosphere, itis preferable to maintain the pressure in the vessel to be constant byintroducing inorganic gas or a volatile blowing agent similar to theabove from the outside in order to facilitate the discharging of thebeads.

Next, the polypropylene resin expanded particles of the secondassociated is molded by using a mold conforming to various conditions(refer to the first associated invention).

For the above expanded molded article, a film can be laminated asrequired (refer to the first associated invention).

The description of the second associated invention has now beencompleted.

THIRD ASSOCIATED INVENTION

Next, the third associated invention is described below The thirdassociated invention relates to a polypropylene resin expanded particlehaving its significantly uniform foam diameter and capable of obtaininga molded article with its excellent surface appearance and mechanicalproperties; a molded article thereof; and a polypropylene resincomposition suitable as a base resin of the molded article and thepolypropylene resin expanded particle.

An expanded molded article obtained from a polypropylene resin expandedparticle is excellent in chemical resistance, shock resistance, andcompression strain recovery or the like, as compared with a moldedarticle made of a polystyrene resin expanded particle. Thus, theexpanded molded article is suitably used as a bumper core material ofautomobiles or the like or as a variety of packaging materials and thelike.

The above polypropylene resin expanded particle contains a polypropyleneresin composition serving as a base resin and a blowing agent.

As the above polypropylene resin composition, from an aspect of itsfoaming applicability or the like, there is employed apropylene-alpha-olefin random copolymer or the like obtained byprimarily copolymerizing alpha-olefin such as ethylene or 1-butene orthe like with propylene. However, even using these copolymers are low indynamic properties, since they are copolymers.

Thus, in order to improve dynamic properties of the polypropylene resincomposition, there have been proposed a method of reducing the contentof comonomer in a copolymer, or alternatively, a method of mixing linearpolyethylene with propylene-alpha-olefin random copolymer (refer topatent document 3). However, with such methods as well, there has been alimitation to improving the dynamic properties of a molded article.

On the other hand, polypropylene itself is essentially a synthetic resinhaving excellent dynamic properties such as rigidity. Thus, whenexpanded particles can be obtained by a polypropylene homopolymer, anexpanded particle molded article with its sufficiently high rigidity canbe obtained. However, in the case where an attempt is made to obtain amolded article by expanded particles composed of a polypropylenehomopolymer, the foaming temperature range or molding range is extremelynarrow, and it is very difficult to precisely control these conditions.Thus, there has been a problem that a fusion failure between particlesoccurs with the obtained molded article or the appearance of the moldedarticle surface is poor. Therefore, in actual industrial production, anexpanded molded article has not been successfully obtained by apolypropylene homopolymer.

However, in recent years, there has been proposed a method in whichpolypropylene expanded article having a syndiotactic structure obtainedby using a so-called metallocene catalyst as a base resin of an expandedarticle (refer to Patent Document 4). With this proposal, it becomespossible to produce an expanded article by a propylene homopolymer.

However, there has been a problem that polypropylene having asyndiotactic structure is low in melting point and is inferior inmechanical properties as compared with polypropylene having an isotacticstructure.

In addition, in Patent Document 5 described later, there has beenproposed a polypropylene resin expanded particle in which an isotacticpolypropylene resin polymerized by using a metallocene polymer catalystis used as a base resin.

In this case, although the foam diameter of expanded particles arecharacterized to be comparatively uniform, dynamic properties of amolded article obtained by using such expanded particles are notsufficient, and further improvement has been desired.

Patent Document 3

-   JP 1982-90027 Unexamined Patent Publication (Kokai) (claims) Patent    Document 4-   JP 1992-224832 Unexamined Patent Publication (Kokai) (claims) Patent    Document 5-   JP 1994-240041 Unexamined Patent Publication (Kokai) (claim 1)

However, in the case where expanded molding has been performed by usingthe above conventional expanded particles, and it has been impossible toobtain a molded article having both significantly uniform foam diameterand excellent surface appearance and mechanical properties.

The third associated invention has beer made in view of such aconventional problem. The object of the third associated invention is toprovide a polypropylene resin expanded particle in which foam diameteris significantly uniform and a molded article with its excellent surfaceappearance and mechanical properties can be obtained; and apolypropylene resin composition which is suitable as the molded articleand a base resin of the polypropylene resin expanded particle resinexpanded particle.

The first aspect of the third associated invention is a polypropyleneresin composition, characterized by comprising:

5% by weight to 95% by weight of a following propylene polymer [A]; and

95% by weight to 5% by weight of a following propylene polymer [B] (thetotal amount of propylene polymers [A] and [B] is 100% by weight),

wherein a propylene polymer [A] has the following requirements (a) to(c)

(a) a structural unit derived from propylene is present in 100 to 85mole %, and a structural unit derived from ethylene and/or alpha-olefinwith 4 to 20 carbons is present in 0 to 15 mole %; (the total amount ofthe structural unit derived from propylene and the structural unitderived from ethylene and/or alpha-olefin with 4 to 20 carbons is 100mol %);

(b) a content of a position irregularity unit based on 2,1-insertion ofa propylene monomer unit in all propylene insertions, which is measuredby 13C-NMR, is 0.5% to 2.0%, and a content of a position irregularityunit based on 1,3-insertion of propylene monomer unit in all propyleneinsertions, which is measured by 13C-NMR, is 0.005% to 0.4%; and

(c) in the case where a melting point is defined as Tm [° C.], and wherea water vapor transmission rate when made into a film is defined as Y[g/m²/24 hr], Tm and Y meet the following formula (1)(−0.20)·Tm+35≦Y≦(−0.33)·Tm+60   Formula (1);and a propylene polymer [B] has only (a) of the above requirements (a)to (c). (claim 13)

The polypropylene resin composition of the third associated contains 5%by weight to 95% by weight of the propylene polymer [A] having the aboverequirements (a) to (c) and 95% by weight to 5% by weight of thepropylene polymer [B] having only requirement (a) of the aboverequirements (a) to (c).

Thus, the above polypropylene resin composition is excellent inmechanical properties.

In addition in the polypropylene resin composition of the thirdassociated invention, when expanded particles are produced using theabove polypropylene resin composition as a base resin, expandedparticles with its significantly uniform foam diameter can be obtained.Thus, when the expanded particles are molded, a molded article with itsexcellent surface appearance and mechanical properties can be obtained.That is, the polypropylene resin composition of the third associatedinvention can be used as an optimal base resin of the polypropyleneresin expanded particle.

The base resin used here means a substrate resin component constitutingthe expanded particle. The expanded particle is made of the above baseresin, other polymer components which is added according to need, andadditives such as a blowing agent, catalyst neutralizing agent,lubricating agent, nucleating agent, and any other resin additive.

The second aspect of the third associated invention is a polypropyleneresin expanded particle characterized in that a polypropylene resincomposition as claimed in any one of claims 8 to 11 is comprised as abase resin (claim 17).

In the third associated invention, the polypropylene resin compositionof the first aspect of the present invention is used as a base resin,and thus, a polypropylene resin expanded particle with its significantlyuniform foam diameter can be obtained. In addition, by using thispolypropylene resin expanded particle, a molded article excellent inmechanical properties such as compression strength or tensile strengthand excellent in a surface appearance can be obtained.

The base resin used here means a substrate resin component constitutingthe above polypropylene resin expanded particle. The above polypropyleneresin expanded particle is made of the above base resin, other polymercomponents which is added according to need, and additives such ascatalyst neutralizing agent, lubricating agent, nucleating agent, andany other resin additive.

A third aspect of the third associated invention is a molded article,made by molding polypropylene resin expanded particles in a mold andhaving density of 0.008 g/cm³ to 0.5 g/cm³, wherein the abovepolypropylene resin expanded particles are that of the above secondinvention. (claim 19)

The molded article of the third associated invention is molded in a moldby using the polypropylene resin expanded particle of second invention,and has the above density.

Thus, the above molded article is excellent in mechanical propertiessuch as compression strength or tensile strength, and is excellent insurface appearance such as smoothness or gloss properties.

In the first aspect of the third associated invention (claim 13), theabove polypropylene resin composition contains a propylene polymer [A]and a propylene polymer [B]. First, the above propylene polymer [A] is apropylene polymer having the above requirements (a) to (c) Now, thepropylene polymer [A] will be described here.

First of all, the above requirement (a) is that a structural unitderived from propylene is present in 100 mol % to 85 mol %, and astructural unit derived from ethylene and/or alpha-olefin with 4 to 20carbons is present in 0 mol % to 15 mol %.

Here, the total amount of the structural unit derived from propylene andthe structural unit derived from ethylene and/or olefin with 4 to 20carbons is 100 mol %.

Therefore, the polypropylene polymer meeting the requirement (a)includes that made of a propylene homopolymer (100 mol %) or that madeof a copolymer of propylene with ethylene and/or alpha-olefin with 4 to20 carbons.

As ethylene and/or alpha-olefin with 4 to 20 carbons, of comonomers,which are copolymerized with propylene, there can be specificallyexemplified: ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or4-methyl-1-butene and the like.

In addition, in the third associated invention, a polypropylene resinobtained by employing monomers which has been hardly polymerized by aconventional Ziegler-Natta catalyst, in copolymerizing with propylene,can be employed as the above propylene polymer [A].

Then, the above polypropylene resin composition containing such apropylene polymer can be used as a base resin for producing expandedparticles.

As these monomers, there can be exemplified one or more kinds of cyclicolefin such as cyclopentene, norbornene,1,4,5,8-dimethano-1,2,3,4,4a,8,8a,5-octahydronaphthalene; non-conjugatediene such as 5-methyl-1,4-hexadiene, 7-methyl-1,6-octadiene; and anaromatic unsaturated compound such as styrene or divinylbenzene.

The propylene polymer [A] for use in the third associated invention is,as in the above requirement (a), a propylene (co)polymer resin whichcontains 85 mol % to 100 mol % of the structural unit derived from thepropylene contained in a propylene polymer, and it is required that thestructural unit derived from ethylene and/or alpha-olefin with 4 to 20carbons is contained at a content of 0 mol % to 15 mol %.

In the case where the structural unit of a comonomer is out of the aboverange, the mechanical properties of the above polypropylene resincomposition such as bending strength or tensile strength aresignificantly lowered. In addition, even if expanded particles arefabricated with the above polypropylene resin composition being a baseresin, desired expanded particles with uniform foam size cannot beobtained. Further, even if the expanded particles are molded, a desiredmolded article cannot be obtained.

Next, as shown in the above requirement (b), the above propylene polymer[A] has 0.5% to 2.0% at a content of a position irregularity unit basedon 2,1-insertion of a propylene monomer unit in all propylene insertionsmeasured by 13C-NMR, and a content of position irregularity unit basedon 1,3-insertion of propylene monomer unit is 0.005% to 0.4%.

The requirement (b) relates to a content of a position irregularity unitof a propylene polymer. Such an irregularity unit has an effect thatcrystalline properties of the propylene polymer is lowered, and exhibitsadvantageous effect that foaming properties are improved.

In the case where the content of position irregularity unit based on theabove 2,1-insertion is lower than 0.5%, in the polypropylene resincomposition of the third associated invention, there is a problem that,when polypropylene expanded particles are fabricated with the abovecomposition as a base resin, the advantageous effect of making uniformthe foam size of expanded particles is reduced. On the other hand, inthe case where 2.0% is exceeded, mechanical properties of a propyleneresin composition as a base resin, for example, bending strength ortensile strength and the like, is lowered. Thus, there is a problem thatthe strengths of expanded particles and a molded article obtainedtherefrom are lowered.

In the case where the content of position irregularity unit based on1,3-insertion is lower than 0.005%, in the polypropylene resincomposition of the third associated invention, there is a problem that,when polypropylene expanded particles are fabricated with the abovecomposition being a base resin, the advantageous effect of makinguniform the foam size of expanded particles is reduced. On the otherhand, in the case where 0.4% is exceeded, mechanical properties of apropylene resin composition as a base resin, for example, bendingstrength or tensile strength and the like, is lowered. Thus, there is aproblem that the strengths of expanded particles and a molded articleobtained therefrom are lowered.

Here, the contents of the structural unit derived from propylene in theabove propylene polymer, the content of the structural unit derived fromethylene and/or alpha-olefin with 4 to 20 carbons in the above propylenepolymer, and the isotactic triad fraction described later are measuredby employing a 13C-NMR technique.

For the 13C-NMR spectrum measurement technique, refer to the above firstassociated invention.

Further, in the third associated invention, the above propylene polymer[A] contains a specific amount of partial structures (I) and (II) in theabove chemical formula 2 which includes a position irregularity unitbased on 2,1-insertion and 1,3-insertion of propylene (refer to thefirst associated invention).

The mm fraction in all polymer chains of the propylene polymer accordingto the third associated invention is expressed by the above mathematicalformula 1 (refer to the first associated invention).

In addition, a content of 2,1-inserted propylene and a content of1,3-inserted propylene with respect to all propylene insertions arecalculated by the above mathematical formula 2 (refer to the firstassociated invention).

Next, with respect to requirement (c), a relationship between watervapor transmission rate and a melting point in the case where apropylene polymer [A] has been made into a film is shown.

That is, in the above propylene polymer [A], in the case where a meltingpoint of the polymer is defined as Tm [° C.] and the water vaportransmission rate when the polymer is molded into a film is defined as Y[g/m²/24 hr], Tm and Y meets the following relational formula (1).(−0.20)·Tm+35≦Y≦(−0.33)·Tm+60   Formula (1)

The above water vapor transmission rate can be measured by JIS K7129“Testing Method for Water Vapor Transmission Rate of Plastic Film andSheeting”.

In the case where the value Y of water vapor transmission rate is withinthe above range, in the polypropylene resin composition of the thirdassociated invention, when polypropylene resin expanded particles or anexpanded molded article is fabricated by using the above composition asa base resin, the foam size of the expanded particles and expandedmolded article are extremely uniform.

In the case where the value Y of water vapor transmission rate exceedsthe range of formula (1) and in the case where the value is lower thanthe range of formula (1), there is a possibility that mechanicalproperties of the polypropylene resin composition of the thirdassociated invention are lowered. When expanded particles are fabricatedwith this polypropylene resin composition being a base resin, thenon-uniformity of foam size in the expanded particles increases. As aresult, in the case where the expanded particles are molded into amolded article, only the molded article with its inferior mechanicalproperties can be obtained.

Although this reason is not clear, it is estimated that a balancebetween impregnation and escape of a blowing agent is associated withthe uniformity of foam diameter, when the blowing agent is impregnatedunder a warming and pressurization, and is discharged to a low pressureatmosphere, thereby producing expanded particles. Further, it isestimated that this balance becomes suitable in the case of using apolypropylene resin composition which contains a propylene polymer suchthat a melting point (Tm) and water vapor transmission rate (Y) meet arelationship indicated in formula (1).

The above propylene polymer [A] can be obtained by using a so-calledmetallocene catalyst, for example.

Now, the above propylene polymer [B] in the first invention of the thirdassociated invention (claim 13) will be described below.

The above propylene polymer [B] is a propylene polymer having only (a)of the above requirements (a) to (c). That is, the above propylenepolymer [B] meets the requirement (a) that the structural unit derivedfrom propylene exists to be 100 mol % to 85 mol % and the structuralunit derived from ethylene and/or alpha-olefin with 4 to 20 carbonsexists to be 0 mol % to 15 mol %, and fails to meet any of the aboverequirements (b) and (c).

The above requirement (a) is same as the requirement [a] of the abovepropylene polymer [A].

Next, it is preferable that the above propylene polymer [A] further havethe following requirement (d) (claim 14).

(d) an isotactic triad fraction at a propylene unit chain part which hasahead-to-tail linkage, which is measured by 13C-NMR, is 97% or more.

In this case, there can be provided advantageous effect that higheruniformity of foam diameter in expanded particles is obtained by usingthe above polypropylene resin composition as a base resin.

That is, as the propylene polymer (A) which is a constituent componentof a resin composition, in addition to the requirements (a) to (c) whichhave been already described, there is used a polymer in which theisotactic triad fraction measured by 13C-NMR (nuclear magneticresonance) technique, of a propylene unit contiguous chain part having ahead-to-tail linkage (that is, a rate of the three propylene unit inwhich each of arbitrary propylene unit 3 contiguous chains in polymerchains is linked in a heat-to-tail manner and the directions of methylbranch in propylene unit are identical) is 97% or more.

Hereinafter, the isotactic triad fraction is properly described as an mmfraction. In the case where the mm fraction is less than 97%, mechanicalproperties of the polypropylene resin composition is lowered. Thus,there is a possibility that the mechanical properties of a moldedarticle composed of expanded particles obtained by using the compositionas a base resin are also lowered.

Further preferably, the above mm fraction is 98% or more.

Next, it is preferable that the above propylene polymer [A] further havethe following requirement (e) (claim 15). (e) the melt flow rate is 0.5g to 100 g/10 minutes.

In this case, the above polypropylene resin composition can be producedwhile the industrially useful production efficiency is maintained.Further, there can be attained advantageous effect that a molded articlecomposed of expanded particles obtained by using this composition as abase resin has its excellent dynamic properties.

In the case where the above melt flow rate (MFR) is lower than 0.5 g/10minutes, there is a possibility that the production efficiency of theabove polypropylene resin composition, in particular, the productivityunder the melting and kneading process described later is lowered. Inaddition, in the case where the MFR exceeds 100 g/10 minutes, there is apossibility that dynamic properties such as compression strength ortensile strength of a molded article obtained by further moldingexpanded particles when the obtained polypropylene resin composition isused as a base resin are lowered. Preferably, the melt flow rate is 1.0g/10 minutes to 50 g/10 minutes. Further preferably, it is 1.0 g/10minutes to 30 g/10 minutes.

Next, it is preferable that the above polypropylene resin compositionexhibits a substantially single melting peak in measurement using adifferential scanning calorimeter (claim 16).

In this case, it means that the above propylene polymer [A] and theabove propylene polymer [B] are dissolved each other, and it exhibitsthat the uniformity of the resin composition is high. As a result, foamdiameter becomes uniform in the expanded resin particles obtained byusing such a polypropylene resin composition as a base resin.

The polypropylene resin composition according to the third associatedinvention is used as a base resin of a material for obtainingpolypropylene resin expanded particles. Further, the polypropylene resinexpanded particles are foamed by filling and heating them in a mold,whereby a molded article can be obtained.

Next, it is preferable that, in the third associated invention (claim16), the above polypropylene resin expanded particles be foamed by usinga blowing agent which meets the following requirement (f) (claim 17) (f)in the case where a critical temperature of the above blowing agent isdefined as Tc [° C.], Tc meets the following formula (2):−90° C.≦Tc≦400° C.   Formula (2)

In this case, there is a tendency that the foam diameter of the obtainedpolypropylene resin expanded particles is uniform. As a result, thedynamic properties of the expanded molded article obtained by using suchexpanded particles are improved.

In the case where Tc is lower than −90° C., there is a possibility thatthe non-uniformity of foam diameter of the obtained polypropylene resinexpanded particles becomes significant. Although the reason is notclear, it is estimated that such non-uniformity is caused by suddenpromotion of foaming.

On the other hand, in the case where Tc is higher than 400° C., there isa possibility that it becomes very difficult to obtain propylene resinexpanded particles with high magnificence, for example, 0.1 g/cm² orless of density.

For a specific example of the above blowing agent, refer to the firstassociated invention.

In addition, among the blowing agents which meet the above formula (2),in the case where the following formula (3) is met, there is anadvantage that special facility or equipment is not required forhandling these blowing agents.0° ≦Tc≦300° C.   Formula (3)

Further, in the case where the following formula (4) is met, in additionto industrial effectiveness described in the previous section, there isadvantageous effect that the foam diameter of the obtained expandedparticles are extremely uniform.30° C.≦Tc≦200° C.   Formula (4)

The above blowing agents may be used alone or in combination of the twoor more.

In the above polypropylene resin expanded particles of the secondinvention of the third associated invention, other polymer components oradditive agents can be mixed with a base resin of the abovepolypropylene resin composition composed of the propylene polymer [A]and polypropylene polymer [B] without departing from advantageous effectof the third associated invention.

For the other polymer component and additive agents, refer to the firstassociated invention.

In the third associated invention, when the propylene polymers [A] and[B] as the above base resins are mixed with each other and when theother component is mixed with the above base resins, although suchmixings can be carried out where the polypropylene base resin is in asolid state, in general, melting and kneading is used. That is, by usinga variety of kneading machines such as a roll, a screw, a Banbury mixer,a kneader, a blender, or a mill, the above propylene polymers or theabove base resin and the other component or the like are kneaded at adesired temperature. After kneading, the product is granulated into anappropriate size of particles suitable to production of expandedparticles.

In addition, it is preferable to use a method for performing melting andkneading in an extruder, followed by extruding in a strand shape akneaded material from a die having small holes mounted at a tip end ofthe extruder, and then, performing cutting at a specified weight or sizeby a cutting machine to obtain resin particles.

In addition, in general, there is no problem with production of expandedparticles when the weight of one resin particle is 0.1 mg to 20 mg. Whenthe weight of one resin particle is in the range of 0.2 mg to 10 mg, andfurther, a dispersion in weight between particles is small, expandedparticles can be easily produced. Further, the density distribution ofthe obtained expanded particles becomes small, and the fillingproperties of expanded resin particles in a mold or the like isimproved.

As a method of obtaining expanded particles, there can be used a methodof impregnating a volatile blowing agent in resin particles, followed byheating and foaming them. Specifically, there can be used methodsdescribed in JP 1974-2183 Examined Patent Publication (Kokoku), JP1981-1344 Examined Patent Publication (Kokoku), DE 1285722 UnexaminedPatent Publication (Kokai), and DE 2107683 Unexamined Patent Publication(Kokai).

After a blowing agent has been impregnated in resin particles, in thecase where heating and foaming are performed, resin particles are put ina pressure vessel which can be closed and released together with avolatile blowing agent. Then, heating is performed at a softeningtemperature or more, of a base resin, and the volatile blowing agent isimpregnated in the resin particles. Thereafter, the content within theclosed vessel is discharged from the closed vessel to a low pressureatmosphere, and then, the solid part is treated to be dried. In thismanner, expanded particles are obtained.

It is preferable that the polypropylene resin expanded particles of thethird associated invention exhibits an endothermic peak with its highertemperature as well as an endothermic peak intrinsic to a base resin ina DSC curve obtained by differential scanning calorimetry (the DSC curveis obtained when 2 mg to 4 mg of expanded particles are heated from 20°C. to 200° C. at a rate of 10° C. per minute by the differentialscanning calorimeter).

Expanded particles in which an endothermic peak intrinsic to the baseresin and an endothermic peak whose temperature is higher than theformer appear in the DSC curve are obtained by controlling the conditionfor foaming the above resin particles, specifically a temperature, apressure, a time and the like for the discharge into a low pressureatmosphere.

In a method of producing expanded particles by discharging the contentof the closed vessel from the closed vessel to a low pressureatmosphere, a decomposition type blowing agent can be kneaded in advancein resin particles, thereby making it possible to obtain the aboveexpanded particles even if the blowing agent is not fed in the pressurevessel.

As the above decomposition type blowing agent, any agent can be usedwhen it is decomposed at a foaming temperature of resin particles, andgenerates gas. Specifically, for example, there can be exemplifiedsodium bicarbonate, ammonium carbonate, an azide compound, an azocompound and the like.

In addition, during heating and foaming, it is preferable that water oralcohol and the like is used as a dispersion medium of resin particles(refer to the first associated invention) When resin particles aredischarged to a low pressure atmosphere, in order to facilitate thedischarge, it is preferable that an inorganic gas or a volatile blowingagent similar to the above is introduced from the outside into theclosed vessel, thereby constantly maintaining the internal pressure ofthe closed vessel.

Next, the polypropylene resin expanded particles of the third associatedinvention is molded by using a mold conforming to various conditions(refer to the first associated invention).

For the above expanded molded article, a film can be laminated asrequired (refer to the first associated invention).

In the above molded article of the third invention of the thirdassociated invention, the density of the molded article is 0.008 g/cm³to 0.5 g/cm³. If the density of the molded article is greater than0.5g/cm, it is impossible to sufficiently provide preferred properties ofthe foamed article such as light weight, shock resistance, or heatresistance. Further, there is a possibility that cost efficiency islowered because of its low expansion ratio.

On the other hand, if the density is smaller than 0.008 g/cm³, there isa tendency that the closed cell ratio is lowered, and mechanicalproperties such as bending strength or compression strength and the likeare insufficient.

The molded articles of the third associated invention is suitable forpackages, toys, automobile parts, helmet core materials, or cushioningpackaging materials and the like.

The description of the third associated invention has now beencompleted.

FOURTH ASSOCIATED INVENTION

Now, the fourth associated invention will be described here.

The fourth associated invention relates to a polypropylene resinexpanded particle which has significantly uniform foam size, whichexhibits excellent fusion properties, which is capable of lowering amolding temperature for obtaining a molded article, and moreover, whichis capable of producing an molded article having an excellent surfaceappearance and mechanical properties, and a molded article using theparticles.

A resin expanded particle has a low thermal conductivity owing to itsclosed cell structure. Thus, this particle is widely used as rawmaterial in obtaining molded articles such as heat insulation materials,cushioning materials, or core materials. In addition, as a thermoplasticresin constituting the above resin expanded particle, in general, thereare used polyethylene, polypropylene, polystyrene or the like.

Among the above described thermoplastic resins, there is an advantagethat an molded article obtained by using a resin expanded particleobtained by using a resin having crystalline properties, i.e.,polyethylene or polypropylene is excellent in chemical resistance orheat resistance, as compared with a molded article obtained by using apolystyrene resin expanded particle.

However, in the case of a high melting point resin represented by apolypropylene resin, since a melting point is as high as 135° C. orabove, a high pressure steam exceeding 0.2 MPaG (hereinafter, referredto as G: Gauge pressure) is required as a pressure for fusing the resinexpanded particles during molding in a mold.

Thus, there is a disadvantage that the molding cost increases, andmoreover, a molding cycle is extended. In addition, in the case of theresin expanded particle made of the above described high melting pointresin, molding cannot be performed in conventional molding machine forexpand able polystyrene. Thus, a molding machine that has a highpressure steam control system and a high mold closing pressure isrequired.

On the other hand, in the case of a polyethylene resin, since a meltingpoint is as low as 125° C. or below, it is sufficient if the steampressure for fusing the resin expanded particles has a low pressure ofless than 0.2 MPaG. Thus, there is provided an advantage that moldingcan be performed even by a molding machine for expand able polystyrenewith almost no change of specification.

However, an molded article of a polyethylenic resin is low in heatresistance, since a base resin has a low melting point. Particularly, inan molded article having high expansion ratio, energy absorptionperformance is small.

Therefore, the molded article of the polyethylene resin can be generallyused only at low expansion ratio, as compared with another moldedarticles of other thermoplastic resins.

In order to solve various problems as described above, there is proposeda resin expanded particle having a specific structure, the resinexpanded particle comprising a core layer in an expanded statecomprising a crystalline thermoplastic resin and a coat layer comprisingan ethylene polymer which is substantially in a non-expanded state.(Patent Document 6)

In this case, a resin expanded particle exhibiting excellent fusionproperties can be obtained even when the heated steam pressure inmolding is low. However, the mechanical strength of a molded articleobtained is not sufficient, and further improvement has been desired.

Patent Document 6

-   JP 1998-77359 Unexamined Patent Publication (Kokai) (pages 2 to 4)

Therefore, the object of the fourth associated invention of the presentapplication is to provide a polypropylene resin expanded particle whichhas significantly uniform foam size and which is capable of obtaining,even if molding is performed with a general-purpose molding machine witha low mold closing pressure, a molded article excellent in surfaceappearance, mechanical properties, fusion between expanded particles andin heat resistance; and a molded article thereof.

The first aspect of the fourth associated invention is a polypropyleneresin expanded particle characterized by comprising:

a core layer in an expanded state comprising of a crystallinethermoplastic resin; and

a coat layer comprising of a thermoplastic resin covering the above corelayer,

wherein the above core layer contains a resin composition as a baseresin characterized by comprising:

5% by weight to 95% by weight of a following propylene polymer [A]; and

95% by weight to 5% by weight of a following propylene polymer [B] (thetotal amount of propylene polymers [A] and [B] is 100% by weight),

wherein a propylene polymer [A] has the following requirements (a) to(c):

(a) a structural unit derived from propylene is present in 100 to 85mole %, and a structural unit derived from ethylene and/or alpha-olefinwith 4 to 20 carbons is present in 0 to 15 mole %; (the total amount ofthe structural unit derived from propylene and the structural unitderived from ethylene and/or alpha-olefin with 4 to 20 carbons is 100mol %);

(b) a content of a position irregularity unit based on 2,1-insertion ofa propylene monomer unit in all propylene insertions, which is measuredby 13C-NMR, is 0.5% to 2.0%, and a content of a position irregularityunit based on 1,3-insertion of propylene monomer unit in all propyleneinsertions, which is measured by 13C-NMR, is 0.005% to 0.4%; and

(c) in the case where a melting point is defined as Tm [° C.], and wherea water vapor transmission rate when made into a film is defined as Y[g/m²/24 hr], Tm and Y meet the following formula (1)(−0.20)·Tm+35≦Y≦(−0.33)·Tm+60   Formula (1)and a propylene polymer [B] has only (a) of the above requirements (a)to (c). (claim 20)

In the polypropylene resin expanded particle of the fourth associatedinvention, the above resin composition containing the propylene polymer[A] and the propylene polymer [B] is contained as a base resin.

Thus, a polypropylene resin expanded particle with high mechanicalstrength of the above core layer can be provided. If such apolypropylene resin expanded particle is molded by a general-purposemolding machine with low mold closing pressure, there can be provided amolded article which is excellent in fusion properties between expandedparticles and the above molded article is excellent in mechanicalproperties such as compression strength and tensile strength and insurface appearance.

In addition, the second aspect of the fourth associated invention is amolded article, made by molding polypropylene resin expanded particlesin a mold and having density of 0.5 g/cm³ to 0.008 g/cm³,

wherein the above polypropylene resin expanded particles are the onewhich is described in the above first aspect of the fourth associatedinvention (claim 27).

The molded article of the fourth associated invention has a density of0.5 g/cm³ to 0.008 g/cm³, and uses that of the above first invention.

Thus, the above molded article can be obtained by heating with a steamof about 0.2 MPaG, is excellent in mechanical properties such ascompression strength and tensile strength, as well as in surfaceappearance such as smoothness and gloss properties.

Therefore, the above molded article is suitable for packages, toys,automobile parts, helmets, core materials, and cushioning packagingmaterials or the like.

If the density of the molded article is greater than 0.5 g/cm³, there isa possibility that preferred characteristics of an expanded article suchas weight reduction, shock absorption properties or heat resistance arenot sufficiently provided, and cost efficiency is lowered because of alow expansion ratio.

On the other hand, if the density is smaller than 0.008 g/cm³, there isa possibility that the closed cell ratio is prone to decrease, andmechanical properties such as bending strength and compression strengthor the like are insufficient.

The polypropylene resin expanded particle of the fourth associatedinvention has a complex structure formed of a core layer and a coatlayer.

In the above first invention of the fourth associated invention (claim20), the above core layer contains a resin composition as a base resinwhich contains the above propylene polymer [A] and the above propylenepolymer [B].

The base resin used here means a substrate resin component constitutingthe above core layer. The core layer is made of the above base resin,other polymer components which is added according to need, and additivessuch as catalyst neutralizing agent, lubricating agent, nucleatingagent, and any other resin additive.

Now, the above propylene polymer [A] will be described here.

The above propylene polymer [A] is a propylene polymer having the aboverequirements (a) to (c).

The above requirement (a) is that a structural unit derived frompropylene is present in 100 mol % to 85 mol %, and a structural unitderived from ethylene and/or alpha-olefin with 4 to 20 carbons ispresent in 0 mol % to 15 mol %.

Here, the total amount of the structural unit derived from propylene andthe structural unit derived from ethylene and/or olefin with 4 to 20carbons is 100 mol %.

Therefore, the polypropylene polymer meeting the requirement (a)includes propylene homol polymer (100 mol %) or a copolymer of propylenewith ethylene and/or alpha-olefin with 4 to 20 carbons.

As ethylene and/or alpha-olefin with 4 to 20 carbons, of comonomers,which are copolymerized with propylene, there can be specificallyexemplified: ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or4-methyl-1-butene and the like.

In addition, in the fourth associated invention, a polypropylene resinobtained by employing monomers which has been hardly polymerized by aconventional Ziegler-Natta catalyst, in copolymerizing with propylene,can be employed as the above propylene polymer [A].

As these monomers, there can be exemplified one or more kinds of cyclicolefin such as cyclopentene, norbornene,1,4,5,8-dimethano-1,2,3,4,4a,8,8a,5-octahydronaphthalene; linearnon-conjugate diene such as 5-methyl-1,4-hexadiene, 7-methyl-1,6-octadiene, 4-ethylidene-8-methyl-1,7-nonadiene or the like; cyclicnon-conjugate polyene such as 5-ethylidene-2-norbornene,dicyclopentadiene, 5-vinyl-2-norbornene, norbornadiene or the like; oraromatic unsaturated compound such as styrene or divinylbenzene. Thesemonomers can be used alone, or in combination of the two or more.

In the above propylene polymer [A] for use in the fourth associatedinvention, as in the above requirement (a), it is required that thestructural unit obtained from propylene in a propylene polymer exist tobe 85 mol % to 100 mol %, and it is required that the structural unitobtained fro methylene and/or alpha-olefin with 4 to 20 carbons existsto be 0 mol % to 15 mol %.

In the case where the structural unit of a comonomer is out of the aboverange, the mechanical properties of the above base resin compositionsuch as bending strength or tensile strength are significantly lowered.In addition, even if expanded particles are fabricated with the aboveresin composition being a base resin, desired expanded particles withexcellent strength and uniform foam size cannot be obtained. Further,even if the expanded particles are molded, a desired molded articlecannot be obtained.

In addition, in the above propylene polymer [A], it is preferable thatthe structural unit obtained from propylene, in particular, exists to be98 mol % to 85 mol %, and that the structural unit obtained fromethylene and/or alpha-olefin with 4 to 20 carbons exists to be 2 mol %to 15 mol % (the total amount of the structural unit obtained frompropylene and the structural unit obtained from ethylene and/oralpha-olefin with 4 to 20 carbons is 100 mol %).

In this case, the structural unit obtained from propylene and thestructural unit obtained from ethylene and/or alpha-olefin with 4 to 20carbons are mandatory components. In addition, there can be attainedadvantageous effect that the above polypropylene resin expandedparticles which contain such a propylene polymer [A] as one component ofthe above core layer are very uniform in the foam size.

Further, in the above propylene polymer [A], the structural unitobtained from propylene can be defined to be 100 mol %.

In this case, the above propylene polymer [A] is a so-called propylenehomopolymer. The above polypropylene resin expanded particles whichcontain such a propylene polymer [A] as one component of the above corelayer are more excellent in strength of the molded article obtained bymolding the particles.

Next, as shown in the above requirement (b), the above propylene polymer[A] is 0.5% to 2.0% at a content of a position irregularity unit basedon 2,1-insertion of a propylene monomer unit in all propylene insertionsmeasured by 13C-NMR, and a content of position irregularity unit basedon 1,3-insertion of propylene monomer unit is 0.005% to 0.4%.

The requirement (b) relates to a content of a position irregularity unitof a propylene polymer. Such an irregularity unit has an effect thatcrystalline properties of the propylene polymer is lowered, and exhibitsadvantageous effect that foaming properties are improved.

In the case where the content of position irregularity unit based on2,1-insertion is lower than 0.5%, in the polypropylene resin compositionof the fourth associated invention, there is a problem that, when thepolypropylene expanded particles are defined as one component of a baseresin forming a core layer of the expanded particles, the advantageouseffect of making uniform the foam size of expanded particles is reduced.On the other hand, in the case where 2.0% is exceeded, mechanicalproperties of a propylene resin composition as a base resin, forexample, bending strength or tensile strength and the like, is lowered.Thus, there is a problem that the strengths of expanded particles and amolded article obtained therefrom are lowered.

In the case where the content of position irregularity unit based on1,3-insertion is lower than 0.005%, there is a problem that, when thepolypropylene expanded particles are defined as one component of a baseresin forming a core layer of the expanded particles, the advantageouseffect of making uniform the foam size of expanded particles is reduced.On the other hand, in the case where the content exceeds 0.4%,mechanical properties of a propylene resin composition as a base resin,for example, bending strength or tensile strength and the like, islowered. Thus, there is a problem that the strength of expandedparticles and a molded article obtained therefrom are lowered.

Here, the contents of the structural unit derived from propylene in theabove propylene polymer, the content of the structural unit derived fromethylene and/or alpha-olefin with 4 to 20 carbons in the above propylenepolymer, and the isotactic triad fraction described later are measuredby employing a 13C-NMR technique.

For the 13C-NMR spectrum measurement technique, refer to the above firstassociated invention.

Further, in the fourth associated invention, the above propylene polymer[A] contains a specific amount of partial structures (I) and (II) in theabove chemical formula 2 which includes a position irregularity unitbased on 2,1-insertion and 1,3-insertion of propylene (refer to thefirst associated invention).

The mm fraction in all polymer chains of the propylene polymer accordingto the fourth associated invention is expressed by the abovemathematical formula 1 (refer to the first associated invention).

In addition, the contents of 2,1-inserted propylene and a rate of1,3-inserted propylene with respect to all propylene insertions arecalculated by the above mathematical formula 2 (refer to the firstassociated invention).

Next, with respect to requirement (c), a relationship between watervapor transmission rate and a melting point in the case where the abovepropylene polymer [A] has been made into a film is shown.

That is, in the above propylene polymer [A], in the case where a meltingpoint of the polymer is defined as Tm [° C.] and the water vaportransmission rate when the polymer is molded into a film is defined as Y[g/m²/24 hr], Tm and Y meets the following relational formula (1).(−0.20)·Tm+35≦Y≦(−0.33)·Tm+60   Formula (1)

The above water vapor transmission rate can be measured by JIS K7129“Testing Method for Water Vapor Transmission Rate of Plastic Film andSheeting”.

In the case where the value Y of the water vapor transmission rate ofthe above propylene polymer [A] is in the above range, the fourthassociated invention is characterized in that the foam size in theexpanded particles of the fourth associated invention is very uniform,and dynamic properties of the molded article obtained by using theexpanded particles are excellent.

In the case where the value Y exceeds a range of formula (1) and in thecase where it is lower than the range of formula (1), the non-uniformityof size of foams in the polypropylene expanded particles of fourthassociated invention increases. As a result, there can be only beobtained an expanded particle with inferior mechanical properties whenmolding the above polypropylene resin expanded particles is effected ina molded article.

Although this reason is not clear, it is presumed that a balance betweenimpregnation and escape of a blowing agent is associated to theuniformity of size of foams when an expanded particle is produced bydischarging it in a low pressure atmosphere; and this balance becomespreferable in the case where a propylene polymer is employed such thatthe melting point (Tm) and water vapor transmission rate (Y) meets arelationship of formula (1) as a polypropylene polymer [A].

The above propylene polymer [A] can be obtained by using a so-calledmetallocene catalyst, for example.

Now, the propylene polymer [B] in the first invention of the fourthassociated invention (claim 20) will be described below.

The above propylene polymer [B] is a propylene polymer having only (a)of the above requirements (a) to (c) That is, the above propylenepolymer [B] meets the requirement (a) that the structural unit derivedfrom propylene exists to be 100 mol % to 85 mol % and the structuralunit derived from ethylene and/or the alpha-olefin with 4 to 20 carbonsexists to be 0 mol % to 15 mol %, and meets neither of the aboverequirements (b) and (c))

The above requirement (a) is same as the requirement [a] of the abovepropylene polymer [A].

Next, it is preferable that the above coat layer comprises of an olefinpolymer in which a melting point lower than either of propylene polymers[A] and [B] forming a core layer or an olefin polymer which showssubstantially no melting point (claim 21).

In this case, there is an advantageous effect that a molded article canbe obtained at a lower temperature.

As an olefin polymer with a lower melting point than the above propylenepolymer [A] and [B], there can be exemplified: high pressure low densitypolyethylene, linear low density polyethylene, linear very low densitypolyethylene; copolymer of ethylene with vinyl acetate, unsaturatedcarboxylic acids or unsaturated carboxylic acid esters, and the like; ora propylene copolymer with ethylene or alpha-olefin or analogous.

In addition, as the above olefin polymer which shows substantially nomelting point, for example, there can be exemplified a rubber orelastomer such as an ethylene-propylene rubber, anethylene-propylene-diene rubber; an ethylene-acrylic rubber; chlorinatedpolyethylene rubber; chlorosulfonated polyethylene rubber, and the like.These rubbers or elastomer can be used alone or in combination of thetwo or more.

Next, it is preferable that the above propylene polymer characterized inthat a propylene polymer of a core layer further has the followingrequirement (d) (claim 22):

(d) an isotactic triad fraction at a propylene unit chain part which hasa head-to-tail linkage, which is measured by13C-NMR, is 97% or more

In this case, there can be provided advantageous effect that theuniformity of the size of foams in the polypropylene resin expandedparticles is further improved.

That is, as the propylene polymer [A] which is a constituent componentof a resin composition for the above core layer, there is used propylenepolymer in which the isotactic triad fraction (that is, a rate of threepropylene unit in which propylene units are bonded with each other in ahead-to-tail manner, of arbitrary three propylene unit in the polymerchains, and the direction of methyl branch in the propylene unit isidentical) measured by 13C-NMR (nuclear magnetic resonance technique),is 97% or more in addition to the already described requirements (a) to(c).

Hereinafter, the isotactic triad fraction is described as an mmfraction. In the case where the mm fraction is less than 97%, there is adanger that the mechanical properties of the resin composition islowered. Thus, there is a possibility that the mechanical properties ofa molded article by molding the composition as abase resin of the corelayer are also lowered.

More preferably, the above mm fraction is 98% or more.

Next, it is preferable that the above propylene polymer [A] further havethe following requirement (e) (claim 23).

(e) a melt flow rate is 0.5 g to 100 g/10 minutes.

In this case, there can be obtained advantageous effect that the abovepolypropylene resin expanded particles can be produced while maintainingproductivity which is useful in commercial production. Further, therecan be attained advantageous effect that a molded article composed ofexpanded particles obtained by using this composition has its excellentphysical properties.

If the above melt flow rate (MFR) is less than 0.5 g/10 minutes, thereis a danger that the productivity of the above polypropylene resinexpanded particles under the melting and kneading process describedlater is lowered. In addition, in the case where the MFR exceeds 100g/10 minutes descried above, there is a danger that dynamic propertiessuch as compression strength or tensile strength of a molded articlederived by employing the above polypropylene resin expanded particlesare lowered. Preferably, the melt flow rate is 1.0 g/10 minutes to 50g/10 minutes, and is further 1.0 g/10 minutes to 30 g/10 minutes.

Next, it is preferable that the above resin composition of the abovecore layer exhibits a substantially single melting peak in measurementusing a differential scanning calorimeter (claim 24).

In this case, it means that the above propylene polymer [A] and theabove propylene polymer [B] are dissolved each other, and it exhibitsthat the uniformity of the resin composition is high. As a result, foamdiameter becomes uniform in the polypropylene resin expanded particlesobtained by using such a resin composition as a base resin of the corelayer.

Next, it is preferable that the above coat layer, the above propylenepolymer [A] and/or the above propylene polymer [B] are blended by 1 partby weight to 100 parts by weight per 100 parts by weight of an olefinpolymer (claim 25).

In this case, adhesive properties between the above core layer and theabove coat layer are improved. As a result, fusion between expandedparticles in the molded article obtained by using the abovepolypropylene resin expanded particles is rigid, and, as a result, thestrength or the like of the molded article is improved.

In the case where a total amount of the above propylene polymers [A] and[B] is lower than 1 part by weight, there is a possibility thatadvantageous effect of improving the degree of fusion between the abovedescribed expanded particles cannot be sufficiently obtained. On theother hand, in the case where the total amount exceeds 100 parts byweight, there is a possibility that a higher steam pressure is requiredto fuse the above expanded particles, thereby obtaining a moldedarticle. More preferably, the total amount is 2 parts by weight to 50parts by weight. Furthermore preferably, the amount is 3 parts by weightto 10 parts by weight.

Next, it is preferable that the above polypropylene resin expandedparticles be foamed by using a blowing agent which meets the followingrequirement (f) (claim 26):

(f) in the case where a critical temperature of the above blowing agentis defined as Tc [° C.], Tc meets the following formula (2).−90° C.≦Tc≦400° C.   Formula (2)

In this case, there is a tendency that the foam diameter of the expandedparticles is more uniform. As a result, the dynamic properties of themolded article obtained by using such expanded particles are improved.In the case where Tc is lower than −90° C., there is a possibility thatthe non-uniformity of foam diameter of the above polypropylene resinexpanded particles becomes significant. Although the reason is notclear, it is estimated that such non-uniformity is caused by suddenprogress of foaming.

On the other hand, in the case where Tc is higher than 400° C., there isa possibility that it becomes very difficult to obtain propylene resinexpanded particles with high magnificence, for example, a density of 0.1g/cm² or less.

For a specific example of the above blowing agent, refer to the firstassociated invention.

In addition, among from the blowing agent which meets the above formula(2), in the case where the following formula (3) is met, there is anadvantage that special facilities or equipment are not requiredespecially when these blowing agents are handled.0° C.≦Tc≦300° C.   Formula (3)

Further, in the case where the following formula (4) is met, there isadvantageous effect that, apart from the engineering effectivenessdescribed previously, the foam diameters of the polypropylene resinexpanded particles obtained are very uniform.30° C.≦Tc≦200° C.   Formula (4)

The above blowing agent may be used alone or in combination of the twoor more.

Additionally, other polymer components or additives can be mixed withthe above resin composition which is a base resin consisting of thepropylene polymers [A] and [B] forming the above core within the rangein which advantageous effect of the fourth associated invention is notdegraded.

For the above other polymer components and additive agents, refer to thefirst associated invention.

In the fourth associated invention, when the propylene polymers [A] and[B] as the above resin composition are mixed with each other and whenthe other component is mixed with the above resin composition, althoughsuch mixings can be carried out where the polypropylene base resin is ina solid state, in general, melting and kneading is used. That is, byusing a variety of kneading machines such as a roll, a screw, a Banburymixer, a kneader, a blender, or a mill, the above propylene polymers orthe above resin composition and the other component or the like arekneaded at a desired temperature. After kneading, the product isgranulated into an appropriate size of particles suitable to productionof polypropylene resin expanded particles.

A raw material for polypropylene resin expanded particles according tothe fourth associated invention is a composite particle which comprisesof a core layer and a coat layer.

As such a specific production method for composite particles, forexample, the following methods can be used.

For example, there can be used a sheath-core shaped composite diedescribed in: JP 1966-16125 Examined Patent Publication (Kokoku); JP1968-23858 Examined Patent Publication (Kokoku); JP 1969-29522 ExaminedPatent Publication (Kokoku); and JP 1985-185816 Unexamined PatentPublication (Kokai) or the like.

In this case, two extruders are used. A thermoplastic resin constitutinga core layer is melted and kneaded by one extruder; a resin constitutinga coat layer is melted and kneaded by the other extruder; and then, asheath-core shaped composite composed of a core layer and a coat layeris discharged out from the die in a strand shape.

It is preferable to use a method for cutting the composite to aspecified weight or size by a strand cutter to obtain columnar pelletshaped resin particles comprising of the core layer and the coat layer.

In general, if the weight of one resin particle is 0.1 mg to 20 mg,there is no problem with production of expanded particles obtained byheating and foaming them. When the weight of one resin particle iswithin the range of 0.2 mg to 10 mg, if a deviation in weight betweenparticles is small, the expanded particles are easily produced, adeviation in density of expanded particles obtained is small, and thefilling properties of resin expanded particles into the mold or the likeare improved.

As methods for obtaining expanded particles from the above resinparticles, there can be used a method of performing heating and foamingafter a volatile blowing agent in the resin particles fabricated asdescribed above has been impregnated in the resin particles; morespecifically, any of the methods described in JP 1974-2183 ExaminedPatent Publication (Kokoku), JP 1981-1344 Examined Patent Publication(Kokoku), DE 1285722 Unexamined Patent Publication (Kokai), and DE2107683 Unexamined Patent Publication (Kokai) or the like.

After a blowing agent has been impregnated in resin particles comprisingof a core layer and a coat layer, in the case where heating and foamingare carried out, resin particles are put into a pressure vessel whichcan be closed or released, together with a volatile blowing agent;heating is carried out at or above the softening temperature of a baseresin in the core layer, and the volatile blowing agent is impregnatedin the resin particles.

Then, after the contents within the vessel are discharged from theclosed vessel into a low pressure, and drying is carried out. In thismanner, polypropylene resin expanded particles can be obtained.

It is preferable that the above resin composition forming a core layerof polypropylene resin expanded particles of the fourth associatedinvention have two or more endothermic peaks in a DSC curve obtained bymeans of differential scanning calorimeter (the DSC curve is obtainedwhen 2 mg to 4 mg of expanded particles are heated from 20° C. to 200°C. at a rate of 10° C. by means of differential scanning calorimeter).This phenomenon arises when a part derived from the resin composition asthe above base resin forms an inherent endothermic peak and anendothermic peak at a higher temperature than the former.

The expanded particles of which two or more endothermic peaks appear onthe above DSC curve are obtained by controlling the condition when theabove composite resin particles are foamed, more specifically, bycontrolling the temperature, the pressure, and a time and the like whendischarging is carried out into a low pressure atmosphere.

In a method of producing expanded particles by discharging the contentsof the vessel into a low pressure atmosphere, when a decomposition typeblowing agent is kneaded in advance in resin particles comprising of thecore layer and coat layer, the blowing agent is added into the pressurevessel, it is possible to obtain the above expanded particles even if noblowing agent is added into a pressure vessel.

As the above mentioned decomposition type blowing agent, any agent canbe used as long as it is decomposed at a foaming temperature of resinparticles and generates a gas. Specifically, for example, sodiumbicarbonate, ammonium carbonate, an azide compound, and an azo compoundand the like can be exemplified.

In addition, during heating and foaming, it is preferable that water oralcohol and the like is used as a dispersion medium of resin particles(refer to the first associated invention)

When resin particles are discharged into a low pressure atmosphere, itis preferable to maintain the pressure in the vessel to be byintroducing inorganic gas or a volatile blowing agent similar to theabove from the outside in order to facilitate the discharging of thebeads.

Next, the polypropylene resin expanded particles of the fourthassociated invention are molded by using a mold under various conditions(refer to the first associated invention).

Furthermore, a film can be laminated on the above molded article asrequired (refer to the first associated invention).

The description of the fourth associated invention has now beencompleted.

FIFTH ASSOCIATED INVENTION

Next, a fifth associated invention is described here.

The fifth associated invention relates to a shock absorber which can beused for a core material or the like for an automobile bumper and ashock-absorbing article having the shock absorber.

At present, as an automobile bumper, there is widely used one comprisedof a core material comprising a synthetic resin expanded article and asynthetic resin skin material which covers the core material. In thisway, by using a synthetic resin expanded article for a core material, anautomobile bumper with its excellent shock absorption properties can beprovided.

In general, in a shock absorber such as a core material for anautomobile bumper, it is required to meet the following three items atthe same time.

-   (1) Energy absorption performance must be excellent;-   (2) Dimensional recovery rate must be excellent; and-   (3) Low density and light weight can be achieved.

In order to achieve this object, there have been proposed the art ofusing polypropylene (refer to Patent Document 7); the art of using anethylene-propylene copolymer (refer to Patent Document 8); and the artof using a 1-butene-propylene copolymer (refer to Patent Document 9), asabase resin of the core material.

In producing a shock absorber such as a core material for an automobilebumper using a polypropylene resin as a base resin, in general, there isused a so-called bead molding technique in which expanded particleswhich contain a polypropylene resin as a base resin are charged andheated in a mold and, thereby foaming them, and particles are mutuallyfused, thereby obtaining a molded article. The polypropylene resinexpanded particle molded article obtained by this method ischaracterized in that it has excellent shock buffering properties orresilience properties, is light in weight, and is small in residualstrain.

Thus, a shock absorber composed of a molded article made ofpolypropylene resin expanded particles has excellent properties ascompared with a shock absorber composed of another material resin.However, with respect to rigidity or energy-absorbing efficiency, asatisfactory result has not necessarily been obtained.

In order to solve the above described problem, there is proposed atechnique for further using a specific propylene homopolymer as a baseresin of a shock absorber such as a core material for a bumper (refer toPatent Document 10).

Expanded particles further containing such a specific propylenehomopolymer as a base resin is characterized in that theenergy-absorbing efficiency of a shock absorber obtained by bead moldingis more excellent than a conventional one.

Patent Document 7

-   JP 1983-221745 Unexamined Patent Publication (Kokai) (claims) Patent    Document 8-   JP 1985-189660 Unexamined Patent Publication (Kokai) (claims) Patent    Document 9-   JP 1990-158441 Unexamined Patent Publication (Kokai) (claims) Patent    Document 10    Brochure of International Application Publication WO98/06777    (claims)

However, in the art of using the above specific propylene homopolymer, ahigh pressure of 3.6 kg/cm² to 4.0 kg/cm² (gauge pressure) is requiredas a steam pressure needed for bead molding. Therefore, there has been aproblem that higher cost is required for molding of a shock absorber,and moreover, a molding cycle is extended.

The fifth associated invention has been made in view of such aconventional problem. The object of the fifth associated invention is toprovide a shock absorber and a shock-absorbing article which can beproduced in accordance with a bead molding technique with a low steampressure and which indicates good shock absorption properties.

The first aspect of the fifth associated invention is a shock absorberobtained by putting and molding expanded particles in a mold,characterized in that the above expanded particle comprises as a baseresin a propylene polymer having the following requirements (a) to (c):

(a) a structural unit derived from propylene is present in 100 to 85mole %, and a structural unit derived from ethylene and/or alpha-olefinwith 4 to 20 carbons is present in 0 to 15 mole %; (the total amount ofthe structural unit derived from propylene and the structural unitderived from ethylene and/or alpha-olefin with 4 to 20 carbons is 100mol %);

(b) a content of a position irregularity unit based on 2,1-insertion ofa propylene monomer unit in all propylene insertions, which is measuredby 13C-NMR, is 0.5% to 2.0%, and a content of a position irregularityunit based on 1,3-insertion of propylene monomer unit in all propyleneinsertions, which is measured by 13C-NMR, is 0.005% to 0.4%; and

(c) in the case where a melting point is defined as Tm [° C.], and wherea water vapor transmission rate when made into a film is defined as Y[g/m²/24 hr], Tm and Y meet the following formula (1)(−0.20)·Tm+35≦Y≦(−0.33)·Tm+60   Formula (1) (claim 28).

The shock absorber of the first invention of the fifth associatedinvention is obtained by molding expanded particles which contains as abase resin a specific propylene polymer having the above requirements(a) to (c).

Thus, the above shock absorber has excellent shock energy-absorbingefficiency and rigidity by utilizing excellent properties which thespecific propylene polymer has.

A reason why the energy-absorbing efficiency is improved in the aboveshock absorber is estimated as follows.

In general, when an impact is applied to a shock absorber, it sconsidered that foams are collapsed while they are compressed, therebyabsorbing impact energy. Therefore, it is estimated that in the shockabsorber the rate of a portion collapsed by low energy is lowered andthe energy absorbed by a shock absorber itself is higher, as thethickness of the wall of foam is uniform.

The shock absorber of the fifth associated invention is obtained bymolding expanded particles which contain as a base resin the propylenepolymer having the above requirements (a) to (c). Then, the aboveexpanded particles which contains the specific propylene polymer as abase resin is very uniform in foam diameter. Thus, it is consideredthat, when a shock absorber is molded, expanded particles with theiruniform foam diameter are foamed, and are fused with each other to forma uniform foam wall, and excellent energy-absorbing efficiency isexhibited as described above.

On the other hand, in a conventional material, the foam size of theexpanded particles obtained by using the material is non-uniform. Evenif such expanded particles are molded to produce a shock absorber, adistribution occurs with the thickness of the foam wall, and a thickpart and a thin part of the foam wall coexist.

When an impact is applied to such a shock absorber, corruption of foamsstarts with low energy at the thin portion of the foam wall. As aresult, a total amount of energy the shock absorber itself can absorb islowered.

In addition, the shock absorber of the fifth associated invention isexcellent in energy-absorbing efficiency, as described above. Thus,during molding thereof, the molding is performed by increasing expansionratio, whereby the weight of the shock absorber can be reduced, and thethickness of the shock absorber can be reduced. Then, even if such anattempt is made to reduce the weight of the above shock absorber in thisway, sufficient energy-absorbing efficiency can be maintained.

In addition, the above shock absorber is obtained by putting expandedparticle which contains as a base resin the specific propylene polymerin a mold and molding them, as described above. Thus, when the aboveexpanded particles are molded by a bead molding technique or the like,for example, the required steam pressure can be lowered. In addition, atime required for cooling in molding can be reduced. That is, an amountof energy required for molding the above shock absorber can be lowered.

In this manner, according to the fifth associated invention, there canbe provided a shock absorber which can be produced in accordance with abead molding technique with a low steam pressure and which exhibits goodshock absorption properties.

A second aspect of the fifth associated invention is a shock-absorbingarticle characterized in that a skin material is provided on a surfaceof the above shock absorber of the first aspect of the fifth associatedinvention (claim 36).

The shock-absorbing article of the fifth associated invention isobtained by providing a skin material on a surface of a shock absorberof the fifth associated invention (claim 28) so as to cover the aboveshock absorber, for example.

Thus, in the above shock-absorbing article, the above shock absorber canabsorb shock energy, as described above, and a skin material provided onthe surface of the shock absorber can improve the strength of theshock-absorbing article.

The other advantageous effect is identical to that of the first aspectof the fifth associated invention.

In the fifth associated invention, the above expanded particle containsa propylene polymer having the above requirements (a) to (c), as a baseresin

The base resin used here means a substrate resin component constitutingthe above expanded particle. The above expanded particle is made of theabove base resin, other polymer components which is added according toneed, and additives such as catalyst neutralizing agent, lubricatingagent, nucleating agent, and any other resin additive.

Hereinafter, the above requirement (a) is first described.

The above requirement (a) is that a structural unit derived frompropylene is present in 100 mol % to 85 mol %, and a structural unitderived from ethylene and/or alpha-olefin with 4 to 20 carbons ispresent in 0 mol % to 15 mol %.

Here, the total amount of the structural unit derived from propylene andthe structural unit derived from ethylene and/or olefin with 4 to 20carbons is 100 mol %.

Therefore, the polypropylene polymer meeting the requirement (a)includes that made of a propylene homopolymer (100 mol %) or that madeof a copolymer of propylene with ethylene and/or alpha-olefin with 4 to20 carbons.

As ethylene and/or alpha-olefin with 4 to 20 carbons, of comonomers,which are copolymerized with propylene, there can be specificallyexemplified: ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or4-methyl-1-butene and the like.

In addition, in the fifth associated invention, a polypropylene basedpolymer obtained by employing monomers which has been hardly polymerizedby a conventional Ziegler-Natta catalyst, in copolymerizing withpropylene, can be employed as the base resin to produce the aboveexpanded particle.

As these monomers, there can be exemplified one or more kinds of cyclicolefin such as cyclopentene, norbornene,1,4,5,8-dimethano-1,2,3,4,4a,8,8a,5-octahydronaphthalene; linearnon-conjugate diene such as 5-methyl-1,4-hexadiene,7-methyl-1,6-octadiene, 4-ethylidene-8-methyl-1,7-nonadiene; cyclicnon-conjugate polyene such as 5-ethylidene-2-norbornene,dicyclopentadiene, 5-vinyl-2-norbornene, and norbornadiene, and anaromatic unsaturated compound such as styrene, or divinylbenzene.

It is required that the propylene polymer for use in the fifthassociated invention is, as in the above requirement (a), a propylene(co)polymer resin which contains 85 mol % to 100 mol % of the structuralunit derived from the propylene contained in a propylene polymer, andthe structural unit derived from ethylene and/or alpha-olefin with 4 to20 carbons is contained at a content of 0 mol % to 15 mol %.

In the case where the structural unit of propylene and the structuralunit of ethylene and/or alpha-olefin as a co-monomer is out of the aboverange, the mechanical properties of the above base resin such as abending strength and a tensile strength are significantly lowered. As aresult, improvement of the rigidity and energy-absorbing efficiency in ashock absorber is not achieved.

In addition, in the above propylene polymer, in particular, it ispreferable that the structural unit derived from propylene is present in98 mol % to 85 mol %, and that the structural unit derived from ethyleneand/or alpha-olefin with 4 to 20 carbons is present in 2 mol % to 15 mol% (the total amount of the structural unit derived from propylene andthe structural unit derived from alpha-olefin with 4 to 20 carbons is100 mol %)

In this case, the above structural unit derived from propylene and theabove structural unit derived from ethylene and/or alpha-olefin with 4to20 carbons are essential ingredients In addition, the above expandedparticles which contain such a propylene polymer as the above base resinare very uniform in their foam diameter. Thus, the above shock absorberobtained by molding these expanded particles are very uniform in thethickness its foam wall, and is more excellent in energy-absorbingefficiency.

In addition, in the above propylene polymer, the structural unit derivedfrom propylene can be set at 100 mol %.

In this case, the above propylene polymer is a so-called propylenehomopolymer. Then, the above shock absorber obtained by using such apropylene polymer is more excellent in its rigidity.

Next, as shown in the above requirement (b), the above propylene polymeris 0.5% to 2.0% at a content of a position irregularity unit based on2,1-insertion of a propylene monomer unit in all propylene insertions,which is measured by 13C-NMR, and a content of position irregularityunit based on 1,3-insertion of propylene monomer unit is 0.005% to 0.4%.

A propylene polymer containing each of these two kinds of positionirregularity units in the above described amount is used as a baseresin, whereby there is achieved advantageous effect that the foamdiameter of expanded particles obtained therefrom is significantlyuniform. Then, the above shock absorber obtained by molding suchexpanded particles has advantageous effect that it is significantly highin rigidity and energy-absorbing efficiency.

In the case where the above content of position irregularity unit basedon 2,1-insertion is lower than 0.5%, or alternatively, in the case wherethe above content of position irregularity unit based on 1,3-insertionis lower than 0.005%, the advantageous effect that the foam diameter ofthe above expanded particles are made uniform is reduced. As a result,there is a problem that the rigidity and energy-absorbing efficiency ofthe shock absorber obtained by molding the above described expandedparticles is lowered.

On the other hand, in the case where the above content of positionirregularity unit based on 2,1-insertion exceeds 2.0%, or alternatively,in the case where the above content of position irregularity unit basedon 1,3-insertion exceeds 0.4%, there is a problem that the mechanicalproperties such as bending strength or tensile strength of the abovepropylene polymer are lowered. As a result, there is a problem that thestrength of the above expanded particles which contain the abovepropylene polymer as a base resin and that of the above shock absorberobtained by molding the expanded particles are lowered.

Here, the contents of the structural unit derived from propylene in theabove propylene polymer, the content of the structural unit derived fromethylene and/or alpha-olefin with 4 to 20 carbons in the above propylenepolymer, and the isotactic triad fraction described later are measuredby employing a 13C-NMR technique.

For the 13C-NMR spectrum measurement technique, refer to the above firstassociated invention.

Further, in the fifth associated invention, the above propylene polymercontains a specific amount of partial structures (I) and (II) in theabove chemical formula 2 which includes a position irregularity unitbased on 2,1-insertion and 1,3-insertion of propylene (refer to thefirst associated invention).

The mm fraction in all polymer chains of the propylene polymer accordingto the fifth associated invention is expressed by the above mathematicalformula 1 (refer to the first associated invention).

In addition, a content of 2,1-inserted propylene and a content of1,3-inserted propylene with respect to all propylene insertions arecalculated by the above mathematical formula 2 (refer to the firstassociated invention).

Next, with respect to requirement (c), a relationship between watervapor transmission rate and a melting point in the case where thepropylene polymer has been made into a film is shown.

That is, in the above propylene polymer, in the case where a meltingpoint of the polymer is defined as Tm [° C.] and the water vaportransmission rate when the polymer is molded into a film is defined asY[g/m²/24 hr], Tm and Y meets the following relational formula (1).(−0.20)·Tm+35≦Y≦(−0.33)·Tm+60   Formula (1)

The above water vapor transmission rate can be measured by JIS K7129“Testing Method for Water Vapor Transmission Rate of Plastic Film andSheeting”.

In the case where a value Y of water vapor transmission rate of theabove propylene polymer is within the above range, the foam diameters inexpanded particles become extremely uniform. As a result, the aboveshock absorber obtained by molding these expanded particles is excellentin rigidity and energy-absorbing efficiency.

In the case where the value Y of water vapor transmission rate is out ofthe range of formula (1), the non-uniformity of foam diameter inexpanded particles increases. As a result, the above shock absorber islowered in mechanical properties and energy-absorbing efficiency.

Although this reason is not clear, it is estimated that a balancebetween impregnation and escape of a blowing agent is associated withthe uniformity of foam diameter when the blowing agent is impregnatedunder a warming and pressurization, and is discharged to a low pressureatmosphere, thereby producing expanded particles Further, it isestimated that this balance becomes suitable in the case of using apropylene polymer such that a melting point (Tm) and water vaportransmission rate (Y) meet a relationship indicated in formula (1).

The propylene polymer meeting the above requirements (a) to (c) can beobtained by using a so-called metallocene catalyst, for example.

In addition, the shock absorber of the fifth associated invention can beobtained to be foamed by charging and heating in a mold the expandedparticles which contain as a base resin a propylene polymer having theabove requirements (a) to (c).

Next, it is preferable that the above propylene polymer further have thefollowing requirement (d) (claim 29).

(d) the isotactic triad fraction at a propylene unit chain part whichhas a head-to-tail linkage, which is measured by 13C-NMR, is 97% ormore.

That is, as the propylene polymer for the base resin, in addition to therequirements (a) to (c) which have been already described, there is useda polymer in which the isotactic triad fraction measured by 13C-NMR(nuclear magnetic resonance) technique, of a propylene unit contiguouschain part having a head-to-tail linkage (that is, a rate of the threepropylene unit in which each of arbitrary propylene unit 3 contiguouschains in polymer chains is linked in a heat-to-tail manner and thedirections of methyl branch in propylene unit are identical) is 97% ormore.

In this case, the uniformity of foam size in the above expanded particleis further improved. Thus, the above shock absorber is improved inenergy-absorbing efficiency.

Hereinafter, the isotactic triad fraction is properly described as an mmfraction. In the case where the mm fraction is less than 97%, mechanicalproperties of the above propylene polymer is lowered. Thus, there is apossibility that the mechanical properties and shock absorptionproperties of the above shock absorber are lowered. Further preferably,the above mm fraction is 98% or more.

Next, it is preferable that the above propylene polymer further have thefollowing requirement (e) (claim 30). (e) the melt flow rate is 0.5 g to100 g/10 minutes.

In this case, the above expanded particles used to obtain the aboveshock absorber can be produced while industrially useful productionefficiency is maintained. Further, the physical properties and shockabsorption properties of the above shock absorber can be improved.

In the case where the above melt flow rate (MFR) is lower than 0.5 g per10 minutes, there is a possibility that the production efficiency of theabove expanded particles, in particular, the productivity under themelting and kneading process described later is lowered. On the otherhand, in the case where the MFR exceeds 100 g/10 minutes, there is apossibility that physical properties such as a compression strength anda tensile strength and energy-absorbing efficiency of the above shockabsorber are lowered. Thus, it is more preferred that the above MFRbe 1. 0 g to 50 g/10 minutes. Further preferably, the rate should be 1.0g to 30 g/10 minutes.

Next, it is preferable that the above expanded particles be foamed byusing a blowing agent which meets the following requirement (f) (claim31).

(f) in the case where the critical temperature of the above blowingagent is defined as Tc [° C.], Tc meets the following formula (2).−90° C.≦Tc≦400° C. Formula (2)

In this case, there is a tendency that the foam diameter of the aboveexpanded particles is more uniform. As a result, the physical propertiesof the shock absorber obtained by using such expanded particles areimproved.

In the case where Tc is lower than −90° C., the no-uniformity of foamdiameter of the expanded particles obtained is significant. Although thereason is not clear, it is estimated that such non-uniformity is causedby sudden foaming.

On the other hand, in the case of where Tc is higher than 400° C., thereis a possibility that it becomes very difficult to obtain an expandedparticle with high magnificence, for example, 0.1 g/cm³ or less ofdensity.

For a specific example of the above blowing agent, refer to the firstassociated invention.

In addition among the blowing agents meeting the above formula (2), inthe case where the following formula (3) is met, there is an advantagethat no special facility or equipment is required for handling theseblowing agents.0° C.≦Tc≦300° C.   Formula (3)

Further, in the case where the following formula (4) is met, there isadvantageous effect that the foam diameter of the expanded particlesobtained becomes very uniform in addition to the industrialeffectiveness described previous section.30° C.≦Tc≦200° C.   Formula (4)

Thus, there is advantageous effect that the above shock absorberobtained by using such expanded particles is more excellent in shockabsorption properties.

The above blowing agents may be used alone, or in combination of the twoor more.

In the fifth associated invention, other polymer components or additivescan be mixed with the above propylene polymer (base resin) withoutdeparting from the advantageous effect of the fifth associatedinvention.

For the above other polymer components and additives, refer to the firstassociated invention.

Although mixing of the other polymer components or additives with theabove base resin can be carried out where the resin is in a fluid stateor solid state, in general, melting and kneading is used. That is, forexample, the above base resins and the other components or the like arekneaded at a desired temperature by using a variety of kneading machinessuch as a roll, a screw, a Banbury mixer, a kneader, a blender, or amill, and the like. After kneading, the product is granulated into anappropriate size of resin particles suitable for production of expandedparticles.

The above resin particles can be obtained by a method of performingmelting and kneading in an extruder, followed by extruding in a strand akneaded material from a die having small holes mounted at the tip end ofthe extruder, and then, cutting the material to a specified weight orsize by a cutting machine.

In general, there is no problem with production of expanded particleswhen the weight of one resin particle is 0.1 mg to 20 mg. When theweight of one resin particle is within the range of 0.2 mg to 10 mg, andfurther when a dispersion in weight between particles is small, theexpanded particles are easily produced, the density distribution ofexpanded particles obtained is small, and the filling properties of theexpanded particles into the mold or the like are improved.

As methods for obtaining expanded particles from the above resinparticles, there can be used a method of heating and foaming afterimpregnating volatile blowing agent in the resin particles fabricated asdescribed above, specifically, for example, methods described in JP1974-2183 Examined Patent Publication (Kokoku), JP 1981-1344 ExaminedPatent Publication (Kokoku), DE 1285722 Unexamined Patent Publication(Kokai), and DE 2107683 Unexamined Patent Publication (Kokai) or thelike.

That is, resin particles are put in a pressure vessel which can becloned and released together with an volatile blowing agent. Then,heating is performed at a temperature equal to or greater than asoftening temperature of the base resin, and the volatile blowing agentis impregnated in the resin particles. Then, the content within theclosed vessel is released from the vessel to a low pressure atmosphere,and thus, drying treatment is performed, whereby expanded particles canbe obtained.

In the above described method, if decomposition type blowing agent iskneaded in advance in resin particles, even if a blowing agent is notfed in a pressure vessel, it is possible to obtain the above expandedparticles.

As the above decomposition type blowing agent, any agent can be usedwhen it is decomposed at a foaming temperature of resin particles andgenerates gas. Specifically, for example, there can be exemplifiedsodium bicarbonate, ammonium carbonate, an azide compound, or an azocompound and the like.

In addition, during heating and foaming, it is preferable that water,alcohol or the like be used as a dispersion medium of resin particles(refer to the first associated invention).

When resin particles are released to a low pressure atmosphere, in orderto facilitate the release, it is preferable to constantly maintain theinternal pressure of the closed vessel by introducing an inorganic gasor a volatile blowing agent which is similar to the above from theoutside to the closed vessel.

Next, it is preferable that the above shock absorber have a crystallinestructure in which a peak inherent to the base resin and a peak athigher temperature than that of the inherent peak appear as endothermicpeaks on a first DSC curve obtained when 2 mg to 4 mg of test specimenscut out from the above shock absorber are heated up to 220° C. at a rateof 10° C./minute by means of a differential scanning calorimeter (claim32).

This phenomenon means that the above shock absorber forms an inherentendothermic peak and an endothermic peak at a higher temperature thanthe former on the above DSC curve.

In this case, there can be provided advantageous effect that therigidity of the shock absorber is improved.

As described above, a shock absorber where an inherent peak and a hightemperature peak appears on a DSC curve can be obtained by fabricatingin advance expanded particles where the inherent peak and the hightemperature peak appear on the above DSC curve, and then, molding theexpanded particles by a molding method or the like described later.

In addition, as described above, expanded particles where an inherentpeak and a high temperature peak appear on the DSC curve can be obtainedby controlling a condition for foaming the above resin particles,specifically a temperature, a pressure, a time and the like forreleasing the particles into a low pressure atmosphere.

When the above shock absorber is fabricated by molding the aboveexpanded particles, the molds which conform with various conditions canbe used (refer to the first associated invention)

In addition, it is referable that the density of the above shockabsorber be 0.02 g/cm³ to 0.45 g/cm³ (claim 33).

In this case, sufficient energy absorption performance and light weightperformance can be compatible with each other.

In the case where the density of the above shock absorber is lower than0.02 g/cm³, there is a possibility that the energy absorptionperformance becomes insufficient.

On the other hand, in the case where the density exceeds 0.45 g/cm³,there is a possibility that light weight performance which is anexcellent feature of the expanded article is not sufficiently attained.

In addition, the above shock absorber can be used as a core material foran automobile bumper or a core material for automobile's interiorarticles and the like. Here, as the automobile's interior articles,there can be exemplified, for example, a dashboard, a console box, aninstrument panel, a door panel, a door trim, a ceiling material, aninterior article of a pillar part, a sun visor, armrest, headrest andthe like.

In addition, it is preferable that the above shock absorber have on itssurface a skin layer with a density which is higher than the insidethereof (claim 34).

In this case, the strength of the above shock absorber can be improvedmore remarkably. Thus, the above shock absorber can be used as is, foran automobile's bumper or an automobile's interior articles and thelike.

The above skin layer can be integrally formed when the above expandedparticles are molded-in a mold, thereby fabricating a shock absorber.

For example, the above skin layer can be formed by partially fusing theabove expanded particles by a heat at a portion which comes into contactwith a wall of the mold when the above expanded particles are molded.Therefore, a component of the above skin layer is identical to that ofthe above expanded particles.

In addition, it is preferable that the above shock absorber be a corematerial for an automobile's bumper (claim 35).

In this case, the excellent shock absorption properties of the aboveshock absorber can be used with the maximum efficiency.

Next, in the above second aspect of the fifth associated invention(claim 36), as the above skin material, for example, there areexemplified: an elastomeric polyolefin sheet; a polystyrene resin filmsuch as OPS (bi-axially oriented polystyrene sheet), heat resistant OPS,or HIPS film; a polypropylene resin film such as CPP (non-orientedpolypropylene film) or OPP (bi-axially oriented polypropylene film), ora polyethylene resin film; a variety of films such as a polyester film;and a variety of skin materials such as a felt or non-woven cloth.

As the above described shock-absorbing article, for example, anautomobile's bumper, an automobile interior articles and the like areexemplified. As the automobile's interior articles, for example, thereare exemplified, for example, a dashboard, a console box, an instrumentpanel, a door panel, a door trim, a ceiling material, an interiorarticle of a pillar part, a sun visor, armrest, headrest and the like.

In addition, it is preferable that the above shock-absorbing article bean automobile's bumper (claim 37) In this case, the excellent shockabsorption properties and strength of the above shock-absorbing articlecan be used with the maximum efficiency.

The description of the fifth associated invention has now beencompleted.

SIXTH ASSOCIATED INVENTION

Next, a sixth associated invention is described here.

The sixth associated invention relates to a shock absorber which can beused for a core material or the like for an automobile bumper and ashock-absorbing article having the shock absorber.

For the prior art, refer to the fifth associated invention.

The sixth associated invention has been made in view of such aconventional problem. The object of the sixth associated invention is toprovide a shock absorber and a shock-absorbing article which can beproduced in accordance with a bead molding technique with a low steampressure and which indicates good shock absorption properties.

The sixth associated invention is a shock absorber obtained by puttingand molding expanded particles in a mold, characterized in that,

in the above expanded particles a resin which comprises a resincomposition containing 5% by weight to 95% by weight of the followingpropylene polymer [A] as a base resin and 95% by weight to 5% by weightof the Following propylene polymer [B] (the total amount of a propylenepolymer [A] and a propylene polymer [B] is 100% by weight) is used as abase resin, and wherein

a propylene polymer [A] has the following requirements (a) to (c):

(a) a structural unit derived from propylene is present in 100 to 85mole %, and a structural unit derived from ethylene and/or alpha-olefinwith 4 to 20 carbons is present in 0 to 15 mole %; (the total amount ofthe structural unit derived from propylene and the structural unitderived from ethylene and/or alpha-olefin with 4 to 20 carbons is 100mol %);

(b) a content of a position irregularity unit based on 2,1-insertion ofa propylene monomer unit in all propylene insertions, which is measuredby 13C-NMR, is 0.5% to 2.0%, and a content of a position irregularityunit based on 1,3-insertion of propylene monomer unit in all propyleneinsertions, which is measured by 13C-NMR, is 0.005% to 0.4%; and

(c) in the case where a melting point is defined as Tm [° C.], and wherea water vapor transmission rate when made into a film is defined as Y[g/m²/24 hr], Tm and Y meet the following formula (1)(−0.20)·Tm+35≦Y≦(−0.33)·Tm+60   Formula (1);and a propylene polymer [B] has only (a) of the above requirements (a)to (c) (claim 38).

The shock absorber of the sixth associated invention is obtained bymolding the above specific expanded particle, and the expanded particleis obtained by using as the above base resin the resin composition whichcontains: the propylene polymer [A] having the above requirements (a) to(c); and the propylene polymer [B] having only (a) of the requirements(a) to (c).

Thus, the above shock absorber is excellent in shock energy-absorbingefficiency and rigidity by utilizing an excellent feature which theabove resin composition has.

A reason why the energy-absorbing efficiency is improved in the aboveshock absorber is estimated as follows.

In general, when an impact is applied to a shock absorber, it isconsidered that foams are collapsed while it is compressed, therebyabsorbing impact energy. Therefore, it is estimated that in the shockabsorber the rate of a portion collapsed by low energy is lowered andenergy absorbed by a shock absorber itself is higher, as the thicknessof the wall of foam is uniform.

The shock absorber of the sixth associated invention is obtained bymolding an expanded particle obtained by using the above specific resincomposition as a base resin. In addition, the above expanded particleswhich contain the above specific resin composition as a base resin arevery uniform in foam diameter.

Thus, when the above shock absorber is molded, it is considered that theexpanded particles with their uniform foam diameter are foamed and fusedwith each other, thereby forming a uniform foam wall, and excellentenergy-absorbing efficiency is exhibited as described above.

On the other hand, in a conventional material, the foam diameters of theexpanded particles obtained by using the material are non-uniform. Evenif such expanded particles are molded to produce a shock absorber, adistribution occurs with the thickness of the foam wall, and a thickpart and a thin part of the foam wall coexist.

When an impact is applied to such a shock absorber, corruption of foamstarts with low energy at the thin portion of the foam wall. As aresult, a total amount of energy the shock absorber itself can absorb islowered.

In addition, the shock absorber of the sixth associated invention isexcellent in energy-absorbing efficiency, as described above. Thus,during molding thereof, the molding is performed by increasing expansionratio, whereby the weight of the shock absorber can be reduced, and thethickness of the shock absorber can be reduced. Then, even if such anattempt to reduce the weight of the above shock absorber is made in thisway, sufficient energy-absorbing efficiency can be maintained.

In addition, the above shock absorber is obtained by putting expandedparticles which contains as a base resin the specific resin compositionin a mold and molding them, as described above. Thus, when the aboveexpanded particles are molded by a bead molding technique or the like,for example, the required steam pressure can be lowered. In addition, atime required for cooling in molding can be reduced. That is, an amountof energy required for molding the above shock absorber can be lowered.

In this manner, according to the sixth associated invention, there canbe provided a shock absorber which can be produced in accordance with abead molding technique with a low steam pressure and which exhibits goodshock absorption properties.

A second aspect of the sixth associated invention is a shock-absorbingarticle characterized in that a skin material is provided on a surfaceof the shock absorber of the first aspect of the sixth associatedinvention (claim 47).

The shock-absorbing article of the second aspect of the sixth associatedinvention is obtained by providing a skin material on a surface of ashock absorber of the first aspect of the sixth associated invention(claim 38) so as to cover the shock absorber, for example.

Thus, in the above shock-absorbing article, the above shock absorber canabsorb shock energy, as described above, and a skin material provided onthe surface of the shock absorber can improve the strength of theshock-absorbing article.

The other advantageous effect is identical to that of the first aspectof the sixth associated invention.

In the sixth associated invention, the above shock absorber is obtainedby molding the above expanded particles, and the expanded particlecontains as a base resin a resin composition which contains the abovepropylene polymer [A] and propylene polymer [B].

The base resin used here means a substrate resin component constitutingthe above expanded particle. The above expanded particle is made of theabove base resin, other polymer components which is added according toneed, and additives such as catalyst neutralizing agent, lubricatingagent, nucleating agent, and any other resin additive.

In addition, the above resin composition, as described above, contains5% by weight to 95% by weight of the above propylene polymer [A] and 95%by weight to 5% by weight of the above propylene polymer [B] (the totalamount of the propylene polymer [A] and the propylene polymer [B] is100% by weight).

In the case where the content of the propylene polymer [A] is lower than5% by weight or in the case where the content of the propylene polymer[B] exceeds 95% by weight, there is a problem that a distribution offoam diameter of the above expanded particles becomes wide, andenergy-absorbing efficiency of the shock absorber is lowered. In thiscase, a high molding steam pressure is required to obtain a shockabsorber having a sufficient degree of fusion. Thus, there is a problemthat the molding time is extended, and the molding cost is increased.

On the other hand, in the case where the content of the propylenepolymer [A] exceeds 95% by weight or in the case where the content ofthe propylene polymer [B] is lower than 5% by weight, there is a problemthat energy-absorbing efficiency of the shock absorber is lowered.

First, the above propylene polymer [A] is described hereinafter.

The propylene polymer [A] is a propylene polymer having the aboverequirements (a) to (c).

The above requirement (a) is that a structural unit derived frompropylene is present in 100 mol % to 85 mol %, and a structural unitderived from ethylene and/or alpha-olefin with 4 to 20 carbons ispresent in 0 mol % to 15 mol %.

Here, the total amount of the structural unit derived from propylene andthe structural unit derived from ethylene and/or olefin with 4 to 20carbons is 100 mol %. Therefore, the polypropylene polymer meeting therequirement (a) includes that made of a propylene homopolymer (100 mol%) or that made of a copolymer of propylene with ethylene and/oralpha-olefin with 4 to 20 carbons.

As ethylene and/or alpha-olefin with 4 to 20 carbons, of comonomers,which are copolymerized with propylene, there can be specificallyexemplified: ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or4-methyl-1-butene and the like.

In addition, in the sixth associated invention, a polypropylene polymerobtained by employing monomers which has been hardly polymerized by aconventional Ziegler-Natta catalyst for co-polymerization with propylenecan also be used as the above propylene polymer [A].

As these monomers, there can be exemplified one or more kinds of cyclicolefin such as cyclopentene, norbornene,1,4,5,8-dimetano-1,2,3,4,4a,8,8a,5-octahydronaphthalene; linearnon-conjugate diene such as 5-methyl-1,4-hexadiene,7-methyl-1,6-octadiene, 4-ethylidene-8-methyl-1,7-nonadiene; cyclicnon-conjugated polyene such as 5-ethylidene-2-norbornene,dicyclopentadiene, 5-vinyl-2-norbornene, and norbornadiene, and anaromatic unsaturated compound such as styrene, or divinylbenzene.

As in the above requirement (a), it is required that the propylenepolymer [A] is a propylene (co-)polymer resin containing 85 mol % to 100mol % of the structural unit derived from propylene contained in apropylene polymer, and the structural unit derived from ethylene and/oralpha-olefin with 4 to 20 carbons is contained at a content of 0 mol %to 15 mol %.

In the case where the structural unit of propylene and the structuralunit of ethylene and/or alpha-olefin as a co-monomer is out of the aboverange, the mechanical properties of the above base resin such as abending strength and a tensile strength are significantly lowered. As aresult, improvement of the rigidity and energy-absorbing efficiency in ashock absorber is not achieved.

In addition, in the propylene polymer [A], in particular, it ispreferable that the structural unit derived from propylene is present in98 mol % to 85 mol %, and that the structural unit derived from ethyleneand/or alpha-olefin with 4 to 20 carbons is present in 2 mol % to 15 mol% (the total amount of the structural unit derived from propylene andthe structural unit derived from alpha-olefin with 4 to 20 carbons is100 mol %).

In this case, the above structural unit derived from propylene and theabove structural unit derived from ethylene and/or alpha-olefin with 4to 20 carbons are essential ingredients In addition, the above expandedparticles which contain such a propylene polymer [A] as the above baseresin are very uniform in their foam diameter. Thus, the above shockabsorber obtained by molding these expanded particles are very uniformin the thickness its foam wall, and is more excellent inenergy-absorbing efficiency.

In addition, in the above propylene polymer [A], the structural unitderived from propylene can be set at 100 mol %.

In this case, the above propylene polymer [A] is so-called propylenehomopolymer. Then, the above shock absorber obtained by using such apropylene polymer [A] is more excellent in its rigidity.

Next, as shown in the above requirement (b), the above propylene polymer[A] is 0.5% to 2.0% at a content of position irregularity unit based on2,1-insertion of a propylene monomer unit in all propylene insertions,which is measured by 13C-NMR, and a content of position irregularityunit based on 1,3-insertion of propylene monomer unit is 0.005% to 0.4%.

This requirement (b) relates to a content of a position irregularityunit of a propylene polymer. Such an irregularity unit has an effectthat crystalline properties of the propylene polymer is lowered, andexhibits advantageous effect that foaming properties are improved.

A propylene polymer [A] containing each of these two kinds of positionirregularity units in the above described amount is used as onecomponent of a base resin, whereby there is achieved advantageous effectthat the foam diameter of expanded particles obtained therefrom issignificantly uniform. Then, the above shock absorber obtained bymolding such expanded particles has advantageous effect that it issignificantly high in rigidity and energy-absorbing efficiency.

In the case where the above content of position irregularity unit basedon 2,1-insertion is lower than 0.5%, or alternatively, in the case wherethe above content of position irregularity unit based on 1,3-insertionis lower than 0.005%, the advantageous effect that the foam diameter ofthe above expanded particles are made uniform is reduced. As a result,there is a problem that the rigidity and energy-absorbing efficiency ofthe shock absorber obtained by molding the above described expandedparticles is lowered.

On the other hand, in the case where the above content of positionirregularity unit based on 2,1-insertion exceeds 2.0%, or alternatively,in the case where the above content of position irregularity unit basedon 1,3-insertion exceeds 0.4%, there is a problem that the mechanicalproperties such as bending strength or tensile strength of the abovepropylene polymer are lowered. As a result, there is a problem that thestrength of the above expanded particles which contain the abovepropylene polymer as a base resin and that of the above shock absorberobtained by molding the expanded particles are lowered.

Here, the contents of the structural unit derived from propylene in theabove propylene polymer, the content of the structural unit derived fromethylene and/or alpha-olefin with 4 to 20 carbons in the above propylenepolymer, and the isotactic triad fraction described later are measuredby employing a 13C-NMR technique.

For 13C-NMR spectrum measurement technique, refer to the above firstassociated invention.

Further, in the sixth associated invention, the above propylene polymer[A] contains a specific amount of partial structures (I) and (II) in theabove the above chemical formula 2 which includes a positionirregularity unit based on 2,1-insertion and 1,3-insertion of propylene(refer to the first associated invention).

The mm fraction in all polymer chains of the propylene polymer [A]according to the sixth associated invention is expressed by the abovemathematical formula 1 (refer to the first associated invention).

In addition, a content of 2,1-inserted propylene and a content of1,3-inserted propylene with respect to all propylene insertions arecalculated by the above mathematical formula 2 (refer to the firstassociated invention).

Next, with respect to requirement (c), a relationship between watervapor transmission rate and a melting point in the case where the abovepropylene polymer [A] has been defined as a film is shown.

That is, in the above propylene polymer [A], in the case where a meltingpoint of the polymer is defined as Tm [° C.] and the water vaportransmission rate when the polymer is molded into a film is defined as Y[g/m²/24hr], Tm and Y meets the following relational formula (1).(−0.20)·Tm+35≦Y≦(−0.33)·Tm+60   Formula (1)

The above water vapor transmission rate can be measured by JIS K7129“Testing Method for Water Vapor Transmission Rate of Plastic Film andSheeting”.

In the case where a value Y of water vapor transmission rate is withinthe above range, the foam diameters in expanded particles becomeextremely uniform. As a result, the above shock absorber obtained bymolding these expanded particles is excellent in rigidity andenergy-absorbing efficiency.

In the case where the value Y of water vapor transmission rate is out ofthe range of formula (1), the non-uniformity of foam diameter inexpanded particles increases. As a result, the above shock absorber islowered in mechanical properties and energy-absorbing efficiency.

Although this reason is not clear, it is estimated that a balancebetween impregnation and escape of a blowing agent is associated withthe uniformity of foam diameter when the blowing agent is impregnatedunder a warming and pressurization, and the resin particles aredischarged to a low pressure atmosphere, thereby producing expandedparticles. Further, it is estimated that this balance becomes suitablein the case of using a resin composition as a base resin containing apropylene polymer such that a melting point (Tm) and water vaportransmission rate (Y) meet a relationship indicated in formula (1).

The above propylene polymer [A] can be obtained by using a so-calledmetallocene catalyst, for example.

Next, the above propylene polymer [B] is described here.

The above propylene polymer [B] is a propylene polymer having only (a)of the above requirements (a) to (c) That is, the above propylenepolymer [B] meets the requirement (a) that the structural unit derivedfrom propylene exists to be 100 mol % to 85 mol % and the structuralunit derived from ethylene and/or alpha-olefin with 4 to 20 carbonsexists to be 0 mol % to 15 mol %, and fails to meet any of the aboverequirements (b) and (c).

The above requirement (a) is same as the requirement [a] of the abovepropylene polymer [A].

In the above sixth associated invention, the above shock absorber can beobtained by charging and heating in a mold the expanded particles whichcontain as a base resin a resin composition containing the propylenepolymer [A] and the propylene polymer [B].

Next, it is preferable that the above propylene polymer [A] further hasthe following requirement (d) (claim 39).

(d) the isotactic triad fraction at a propylene unit chain part whichhas a head-to-tail linkage, which is measured by 13C-NMR, is 97% ormore.

That is, as the propylene polymer [A], in addition to the requirements(a) to (c) which have been already described, there is used a polymer inwhich the isotactic triad fraction measured by 13C-NMR (nuclear magneticresonance technique), of a propylene unit contiguous chain part having ahead-to-tail linkage (that is, a rate of three propylene unit in whicheach of arbitrary propylene unit in polymer chains is linked in aheat-to-tail manner and the directions of methyl branch in propyleneunit are identical) is 97% or more.

In this case, the uniformity of foam size in the above expanded particleis further improved. Thus, the above shock absorber is improved inenergy-absorbing efficiency.

Hereinafter, the isotactic triad fraction is described as an mmfraction. In the case where the mm fraction is less than 97%, mechanicalproperties of the resin composition as the above base resin is lowered.Thus, there is a possibility that the mechanical properties and shockabsorption properties of the above shock absorber are lowered. Furtherpreferably, the above mm fraction is 98% or more.

Next, it is preferable that the above propylene polymer [A] further havethe following requirement (e). (claim 40)

(e) the melt flow rate is 0.5 g to 100 g/10 minutes.

In this case, the above expanded particles used to obtain the aboveshock absorber can be produced while industrially useful productionefficiency is maintained. Further, the physical properties and shockabsorption properties of the above shock absorber can be improved.

In the case where the above melt flow rate (MFR) is lower than 0.5 g per10 minutes, there is a possibility that the production efficiency of theabove expanded particles, in particular, the productivity under themelting and kneading process described later is lowered. On the otherhand, in the case where the MFR exceeds 100 g/10 minutes, there is apossibility that physical properties such as a compression strength anda tensile strength; and energy-absorbing efficiency of the above shockabsorber are lowered. Thus, it is more preferred that the above MFR be1.0 g to 50 g/10 minutes. Further preferably, the rate should be 1.0 gto 30 g/10 minutes.

Next, it is preferable that the above expanded particles be foamed byusing a blowing agent which meets the following requirement (f) (claim41).

(f) in the case where the critical temperature of the above blowingagent is defined as Tc [° C.], Tc meets the following formula (2).90° C.≦Tc≦400° C.   Formula (2)

In this case, there is a tendency that the foam diameter of the aboveexpanded particles is more uniform. As a result, the physical propertiesof the shock absorber obtained by using such expanded particles areimproved.

In the case where Tc is lower than −90° C., the no-uniformity of foamdiameter of the above expanded particles is significant. Although thereason is not clear, it is estimated that Such non-uniformity is causedby sudden foaming.

On the other hand, in the case of where Tc is higher than 400° C., thereis a possibility that it becomes very difficult to obtain an expandedparticle with high expansion ratio, for example, 0.1 g/cm³ or less ofdensity.

For a specific example of the above blowing agent, refer to the firstassociated invention.

In addition among the blowing agents meeting the above formula (2), inthe case where the following formula (3) is met, there is an advantagethat no special facility or equipment is required for handling theseblowing agents.0° C.≦Tc≦300° C.   Formula (3)

Further, in the case where the following formula (4) is met, there isadvantageous effect that the foam diameter of the expanded particlesobtained becomes very uniform in addition to the industrialeffectiveness described previous section.30° C.≦Tc≦200° C.   Formula (4)

Thus, there is advantageous effect that the above shock absorberobtained by using such expanded particles is more excellent in shockabsorption properties.

The above blowing agents may be used alone, or in combination of the twoor more.

In the sixth associated invention, other polymer components or additivescan be mixed with the above propylene composition containing thepropylene polymer [A] and the propylene polymer [B] without departingfrom the advantageous effect of the sixth associated invention.

For the above other polymer components and additives, refer to the firstassociated invention.

Although mixing of the above propylene polymer [A] with the abovepropylene polymer [B] or mixing of the other polymer components oradditives with the above base resin can be carried out where the resinis in a fluid state or solid state, in general, melting and kneading isused. That is, for example, the above base resins and the othercomponents or the like are kneaded at a desired temperature by using avariety of kneading machines such as a roll, a screw, a Banbury mixer, akneader, a blender, or a mill, and the like. After kneading, the productis granulated into an appropriate size of resin particles suitable forproduction of expanded particles.

Resin particles can be obtained by a method of performing melting andkneading in an extruder, followed by extruding in a strand a kneadedmaterial from a die having a minutely small holes mounted at the tip endof the extruder, and then, cutting the material to a specified weight orsize by a cutting machine.

In general, there is no problem with production of expanded particleswhen the weight of one resin particle is 0.1 mg to 20 mg. When theweight of one resin particle is within the range of 0.2 mg to 10 mg, andfurther when a dispersion in weight between particles is small, theexpanded particles are easily produced, the density distribution ofexpanded particles obtained is small, and the filling properties of theexpanded particles into the mold or the like are improved.

As methods for obtaining expanded particles from the above resinparticles, there can be used a method of heating and foaming afterimpregnating volatile blowing agent in the resin particles fabricated asdescribed above, specifically, for example, methods described in JP1974-2183 Examined Patent Publication (Kokoku), JP 1981-1344 ExaminedPatent Publication (Kokoku), DE 1285722 Unexamined Patent Publication(Kokai), and DE 2107683 Unexamined Patent Publication (Kokai) or thelike.

That is, resin particles are put in a pressure vessel which can beclosed and released together with a volatile blowing agent. Then,heating is performed at a temperature equal to or above the softeningtemperature of the base resin, and the volatile blowing agent isimpregnated in the resin particles. Then, the content within the closedvessel is released from the vessel to a low pressure atmosphere, andthus, drying treatment is performed, whereby expanded particles can beobtained.

In the above described method, if decomposition type blowing agent iskneaded in advance in resin particles, even if a blowing agent is notfed in a pressure vessel, it is possible to obtain the above expandedparticles.

As the above decomposition type blowing agent, any agent can be usedwhen it is decomposed at a foaming temperature of resin particles andgenerates gas. Specifically, for example, there can be exemplifiedsodium bicarbonate, ammonium carbonate, an azide compound, or an azocompound and the like.

In addition, during heating foaming, it is preferable that water,alcohol or the like be used as a dispersion medium of resin particles(refer to the first associated invention)

When resin particles are released to a low pressure atmosphere, in orderto facilitate the release, it is preferable to constantly maintain theinternal pressure of the closed vessel by introducing an inorganic gasor a volatile blowing agent which is similar to the above from theoutside to the closed vessel.

Next, it is preferable that the above shock absorber have a crystallinestructure in which a peak inherent to the base resin and a peak athigher temperature than that of the inherent peak appear as endothermicpeaks on a first DSC curve obtained when 2 mg to 4 mg of test specimenscut out from the above shock absorber are heated up to 220° C. at a rateof 10° C./minute by means of a differential scanning calorimeter. (claim42).

This phenomenon means that the above shock absorber forms an inherentendothermic peak and an endothermic peak at a higher temperature thanthe former on the above DSC curve.

In this case, there can be provided advantageous effect that therigidity and the shock absorption performance of the shock absorber areimproved as compared with the shock absorber in which no hightemperature endothermic peak exists.

As described above, a shock absorber where an inherent peak and a hightemperature peak appears on a DSC curve can be obtained by fabricatingin advance expanded particles where the inherent peak and the hightemperature peak appear on the above DSC curve, and then, molding theexpanded particles by a molding method or the like described later.

In addition, as described above, expanded particles where an inherentpeak and a high temperature peak appear on the DSC curve can be obtainedby controlling a condition for foaming the above resin particles,specifically a temperature, a pressure, a time and the like forreleasing the particles into a low pressure atmosphere.

Next, it is preferable that the above inherent peak is substantiallysingle (claim 43).

This means that the propylene polymer [A] and the propylene polymer [B]are dissolved each other, and indicates that the uniformity of the resincomposition is high. In this case, energy-absorbing efficiency of theabove shock absorber can be improved more remarkably.

Next, when the above shock absorber is fabricated by molding the aboveexpanded particles, the molds which conform with various conditions canbe used (refer to the first associated invention).

In addition, it is preferable that the density of the above shockabsorber is 0.02 g/cm3 to 0.45 g/cm³ (claim 44).

In this case, sufficient energy absorption performance and light weightperformance can be compatible with each other.

In the case where the density of the above shock absorber is lower than0.02 g/cm³, there is a possibility that the energy absorptionperformance becomes insufficient.

On the other hand, in the case where the density exceeds 0.45 g/cm³,there is a possibility that light weight performance which is anexcellent feature of the expanded article is not sufficiently attained.

In addition, the above shock absorber can be used as a core material foran automobile bumper or a core material for automobile's interiorarticles and the like. Here, as the automobile's interior articles,there can be exemplified, for example, a dashboard, a console box, aninstrument panel, a door panel, a door trim, a ceiling material, aninterior article of a pillar part, a sun visor, armrest, headrest andthe like.

In addition, it is preferable that the above shock absorber have on itssurface a skin layer with a density which is higher than the insidethereof (claim 45).

In this case, the strength of the above shock absorber can be improvedmore remarkably. Thus, the above shock absorber can be used as is, foran automobile's bumper or an automobile's interior articles and thelike.

The above skin layer can be integrally formed when the above expandedparticles are molded in a mold, thereby fabricating a shock absorber.

For example, the above skin layer can be formed by partially fusing theabove expanded particles by a heat at a portion which comes into contactwith a wall of the mold when the above expanded particles are molded.Therefore, a component of the above skin layer is identical to that ofthe above expanded particles.

In addition, it is preferable that the above shock absorber be a corematerial for an automobile's bumper (claim 46).

In this case, the excellent shock absorption properties of the aboveshock absorber can be used with the maximum efficiency.

Next, in the above second aspect of the sixth associated invention(claim 47), as the above skin material, for example, there areexemplified: an elastomeric polyolefin sheet; a polystyrene resin filmsuch as OPS (bi-axially oriented polystyrene sheet), heat resistant OPS,or HIPS film; a polypropylene resin film such as CPP (non-orientedpolypropylene film) or OPP (bi-axially oriented polypropylene film), ora polyethylene resin film; a variety of films such as a polyester film;and a variety of skin materials such as a felt or non-woven cloth.

As the above described shock-absorbing article, for example, anautomobile's bumper, an automobile interior articles and the like areexemplified. As the automobile's interior articles, for example, thereare exemplified, for example, a dashboard, a console box, an instrumentpanel, a door panel, a door trim, a ceiling material, an interiorarticle of a pillar part, a sun visor, armrest, headrest and the like.

In addition, it is preferable that the above shock-absorbing article bean automobile's bumper (claim 48) In this case, the excellent shockabsorption properties and strength which the above shock-absorbingarticle has can be used with the maximum efficiency.

The description of the sixth associated invention has now beencompleted.

SEVENTH ASSOCIATED INVENTION

Now, the seventh associated invention is described below.

The seventh associated invention relates to a polypropylene resin moldedarticle used for a heat insulation material, a cushioning packagingmaterial, a transport box, bumper core material for automobiles, and anautomobile part or the like.

An expanded molded article based on a polypropylene resin is excellentin chemical resistance, heat resistance, and strain recovery aftercompression, as compared with an expanded molded article of apolystyrene resin. This expanded molded article is widely used: for acushioning packaging material and a transport box; for automobile'smembers such as automobile bumper core materials, pillar, platform, andside impact material; for transportation molded articles such as apellet material and a toolbox. In addition, the polypropylene resinexpanded molded article is excellent in heat resistance and compressionstrength, as compared with an expanded molded article based on apolyethylene resin.

Thus, the polypropylene resin expanded molded article is, in particular,used for a member requiring use under a high temperature or strength.

Among a variety of the above described applications, in particular, in ause as a heat insulation material or structural part, it is requiredthat a water vapor transmission characteristic is low in addition to thefact that heat resistance and compression strength are high.

In order to achieve this object, for example, there is proposed atechnique for fusing a film which has moisture-proofness on a surface ofa molded article (refer to Patent Document 11).

Patent Document 11

-   JP 1988-212543 Unexamined Patent Publication (Kokai) (claims)    However, in the above technique of using a film having    moisture-proof properties, an additional process for fusing the    above film is required, and thus, there has been a problem that    higher cost occurs. Further, because of the presence of the above    film per se, the damage resistance properties of a final molded    article are lowered. As a result, there has been a disadvantage that    the appearance of a molded article is degraded. Therefore, there has    been a demand for a material indicative of a low water vapor    transmission characteristic with a single expanded molded article.

The seventh associated invention has been made in view of such aconventional problem. The object of the seventh associated invention isto provide a propylene resin expanded molded article which is excellentin heat resistance and strength and which is lower in water vaportransmission and moisture permeability, and is excellent inmoisture-proofness.

The first aspect of the seventh associated invention is a polypropyleneresin expanded molded article obtained by heating and molding anexpanded particle which comprises as a base resin a propylene polymerhaving the following requirements (a) to (c), characterized in that theabove a polypropylene resin expanded molded article having the followingrequirement (d) (claim 49):

(a) a structural unit derived from propylene is present in 100 to 85mole %, and a structural unit derived from ethylene and/or alpha-olefinwith 4 to 20 carbons is present in 0 to 15 mole %; (the total amount ofthe structural unit derived from propylene and the structural unitderived from ethylene and/or alpha-olefin with 4 to 20 carbons is 100mol %);

(b) a content of a position irregularity unit based on 2,1-insertion ofa propylene monomer unit in all propylene insertions, which is measuredby 13C-NMR, is 0.5% to 2.0%, and a content of a position irregularityunit based on 1,3-insertion of propylene monomer unit in all propyleneinsertions, which is measured by 13C-NMR, is 0.005% to 0.4%; and

(c) in the case where a melting point is defined as Tm [° C.], and wherea water vapor transmission rate when made into a film is defined as A[g/m²/24 hr], Tm and A meet the following formula (1)(−0.20)·Tm+35≦A≦(−0.33)·Tm+60   Formula (1);and

a propylene polymer [B] has only (a) of the above requirements (a) to(c); and

(d) a rate of water vapor transmission Y [g/m²/hour] measured inconformity with ASTM E-96 and a density X [g/cm³] of the polypropyleneresin expanded molded article meets the following formula (2):Y≦(43.6)·X ²−(4.5)·X+0.15   Formula (2)

The polypropylene resin expanded molded article of the seventhassociated invention is obtained by using expanded particles when apropylene polymer having the above requirements (a) to (c) is used as abase resin. In addition, the rate of water vapor transmission Y anddensity X meets the above formula (2).

Thus, the above polypropylene resin expanded molded article exhibitsvery low moisture permeability and a water vapor transmissioncharacteristic while it maintains excellent heat resistance and strengthspecific to a propylene resin.

Therefore, the above polypropylene resin expanded molded article issuitable to be used for such as a heat insulation material, anarchitectural structural member, or a packaging material and the like.

In addition, the above polypropylene resin expanded molded article hasan excellent feature that the water vapor transmission characteristicand moisture permeability are low. Thus, it is possible to reduce thethickness and density of the polypropylene resin expanded molded articlerequired to achieve predetermined moisture-proof properties than aconventional one.

In the above polypropylene resin expanded molded article, although areason why the rate of water vapor transmission is lowered as comparedwith a molded article using a conventional raw material is not clear,the reason is estimated as follows.

That is, the polypropylene resin expanded molded article of the seventhassociated invention, as described above, is obtained by molding theabove expanded particle which contains a specific propylene polymer as abase resin. Thus, the above polypropylene resin expanded molded articleis significantly uniform in size of its foam diameter. That is, theuniformity of thickness of the wall of foams is high.

In the case where such a polypropylene resin expanded molded article isused in an architectural use or the like, for example, the polypropyleneresin expanded molded article is inserted between structural members,and is used as a heat insulation material or the like. At this time, inthe case where there is a difference in water vapor pressure on bothsides of the above polypropylene resin expanded molded article,transport of water vapor takes place. This water vapor is primarilyconsidered as passing by diffusing through the foam wall of the abovepolypropylene resin expanding molded article.

Therefore, if a thick part and a thin part coexist on the foam wall,vapor transmits the thin part more easily as compared with the thickpart. Thus, the vapor passes through such thin part.

On the other hand, the polypropylene resin expanded molded article ofthe seventh associated invention is uniform in the thickness foam wall.Thus, there are a few parts through which vapor easily passes. As aresult, it is estimated that the water vapor transmission characteristicof the entire molded article is lowered.

In addition, the above polypropylene resin expanded molded article canbe produced by a general bead molding technique, for example. Thus, theabove polypropylene resin expanded molded article can be obtained withease and at a low cost without requiring specific facility or the like.

Further, the above polypropylene resin expanded molded article isobtained by molding expanded particles which contain a specificpropylene polymer as abase resin, as described above.

Thus, when the above expanded particles are molded by a bead moldingtechnique or the like, for example, a required steam pressure can bereduced In addition, a time required for cooling during molding can bereduced. That is, an amount of energy required for molding the abovepolypropylene resin expanded molded article can be reduced.

In this manner, according to the seventh associated invention, there canbe provided a propylene resin expanded molded article which is excellentin heat resistance and strength and which is low in water vaportransmission and moisture permeability, and is excellent inmoisture-proof properties.

In the seventh associated invention, the above expanded particlecontains a propylene polymer having the above requirements (a) to (c) asa base resin.

The base resin used here means a base resin component constituting theabove expanded particles. The above expanded particle may contain otherpolymer components to be added according to need, and additives such asa blowing agent, catalyst neutralizing agent, lubricating agent,nucleating agent, and any other resin additive.

Now, the above requirement (a) is first described here.

First of all, the above requirement (a) is that a structural unitderived from propylene is present in 100 mol % to 85 mol %, and astructural unit derived from ethylene and/or alpha-olefin with 4 to 20carbons is present in 0 mol % to 15 mol %

Here, the total amount of the structural unit derived from propylene andthe structural unit derived from ethylene and/or olefin with 4 to 20carbons is 100 mol %.

Therefore, the polypropylene polymer meeting the requirement (a)includes that made of a propylene homopolymer (100 mol %) or that madeof a copolymer of propylene with ethylene and/or alpha-olefin with 4 to20 carbons.

As ethylene and/or alpha-olefin with 4 to 20 carbons, of comonomers,which are copolymerized with propylene, there can be specificallyexemplified: ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or4-methyl-1-butene and the like.

In addition, in the seventh associated invention, a propylene polymerobtained by employing monomers which has been hardly polymerized by aconventional Ziegler-Natta catalyst, in copolymerizing with propylene,can be employed as a base-resin for producing the above expandedparticle.

As such monomers, there can be exemplified at least one or more kinds ofthe followings: cyclopentene, norbornene,1,4,5,8-dimethano-1,2,3,4,4a,8,8a,5-octahydronaphthalene; linearnon-conjugated diene such as 5-methyl-1,4-hexadiene, 7-methyl-1, or6-octadiene, 4-ethylidene-8-methyl-1,7-nonadiene or the like; cyclicnon-conjugate polyene such as 5-ethylidene-2-norbornene,dicyclopentadiene, 5-vinyl-2-norbornene, norbornadiene or the like; oraromatic unsaturated compound such as styrene or divinylbenzene or thelike.

The propylene polymer for use in the seventh associated invention is apropylene (co) polymer resin which contains 85 mol % to 100 mol % of thestructural unit derived from propylene as is described in the aboverequirement (a), in the propylene polymer. In addition, it is requiredthat the structural unit derived from ethylene and/or alpha-olefin with4 to 20 carbons is contained at a content of 0 mol % to 15 mol %.

In the case where a structural unit of a comonomer is out of the aboverange, the mechanical properties of the above propylene polymer such asbending strength or tensile strength are significantly lowered. Inaddition, even if expanded particles are fabricated with the abovepropylene polymer being a base resin, desired expanded particles withhigh strength and uniform foam size cannot be obtained. Further, even ifthe expanded particles are molded, a desired polypropylene based resinmolded article cannot be obtained.

In addition, in the above propylene polymer, in particular, it ispreferable that the structural unit derived from propylene exists to be99.5 mol % to 85.0 mol % and/or the structural unit derived fromethylene and/or alpha-olefin with 4 to 20 carbons exists to be 0.5 mol %to 15.0 mol % (the total amount of the structural unit derived frompropylene and the structural unit derived from ethylene and/oralpha-olefin with 4 to 20 carbons is 100 mol %).

In this case, the structural unit derived from propylene and thestructural unit derived from ethylene and/or alpha-olefin with 4 to 20carbons are mandatory components. In addition, the above expandedparticles containing such a propylene polymer as the above base resinare very uniform in their foam size. Thus, the above polypropylene resinexpanded molded article obtained by molding the expanded particles isvery uniform in its foam wall, and is lower in water vapor transmission.

In addition, in the above propylene polymer, the structural unit derivedfrom propylene can be set at 100 mol %.

In this case, the above propylene polymer is obtained as a so-calledpropylene homopolymer. The above polypropylene resin expanded moldedarticle obtained by using such a propylene polymer is more excellent inits strength.

Next, as shown in the above requirement (b), the above propylene polymeris 0.5% to 2.0% at a content of a position irregularity unit based on2,1-insertion of a propylene monomer unit in all propylene insertionsmeasured by 13C-NMR, and a content of position irregularity unit basedon 1,3-insertion of propylene monomer unit is 0.005% to 0.4%.

The requirement (b) relates to a content of a position irregularity unitof a propylene polymer. Such an irregularity unit has an effect thatcrystalline properties of the propylene polymer is lowered, and exhibitsadvantageous effect that foaming properties are improved.

In the case where the content of position irregularity unit based on2,1-insertion is lower than 0.5% or in the case where the content ofposition irregularity unit based on 1,3-insertion is lower than 0.005%,the advantageous effect of making uniform the foam size of the expandedparticles is reduced. As a result, there is a problem that the degree ofmoisture-proofness of the above polypropylene resin expanded moldedarticle obtained by molding the above expanded particles is improved.

On the other hand, in the case where the content of positionirregularity unit based on 2,1-insertion exceeds 2.0% or in the casewhere the content of position irregularity unit based on 1,3-insertionexceeds 0.4%, there is a problem that mechanical properties such as abending strength or tensile strength of the above propylene polymer arelowered.

Here, the contents of the structural unit derived from propylene in theabove propylene polymer, the content of the structural unit derived fromethylene and/or alpha-olefin with 4 to 20 carbons in the above propylenepolymer, and the isotactic triad fraction described later are measuredby employing a 13C-NMR technique.

For the 13C-NMR spectrum measurement technique, refer to the above firstassociated invention.

Further, in the seventh associated invention, the above propylenepolymer contains a specific amount of partial structures (I) and (II) inthe above chemical formula 2 which includes the position irregularityunit based on 2,1-insertion and 1,3-insertion of propylene (refer to thefirst associated invention).

The mm fraction of all polymer chains of the propylene polymer accordingto the seventh associated invention is expressed by the abovemathematical formula 1 (refer to the first associated invention).

In addition, a content of 2,1-inserted propylene and a content of1,3-inserted propylene with respect to all propylene insertions arecalculated by the above mathematical formula 2 (refer to the firstassociated invention).

Next, in the requirement (c), a relationship between water vaportransmission rate and a melting point in the case where the abovepropylene polymer has been made into a film is shown.

That is, in the above propylene polymer, in the case where a meltingpoint of the polymer is defined as Tm [° C.] or the water vaportransmission rate when the polymer is molded into a film is defined as A[g/m²/24 hr], Tm and A meets the following relational formula (1).(−0.20)·Tm+35≦A≦(−0.33)·Tm+60   Formula (1)

The above water vapor transmission rate can be measured by the JIS K7129“Testing Methods for Water Vapor Transmission Rate of Plastic Film andSheeting”.

In the case where the value A of the water vapor transmission rate ofthe above propylene polymer is in the above range, the foam diameter inthe above expanded particles is extremely uniform. As a result, theabove polypropylene resin expanded molded article obtained by using theexpanded particles are excellent in dynamic properties such as heatresistance and strength.

In the case where the value A of the water vapor transmission ratedeviates from the range of formula (1), the non-uniformity of size offoam in the above expanded particles increases. As a result, themechanical properties of the above polypropylene resin expanded moldedarticle are lowered.

Although this reason is not clear, it is estimated that a balance ofimpregnation and escape of a blowing agent is associated with theuniformity of foam size when the blowing agent is impregnated under awarming and pressurization, and the resin particles are discharged to alow pressure atmosphere, thereby producing expanded particles. Further,it is estimated that this balance becomes suitable in the case of usinga propylene polymer such that a melting point (Tm) and water vaportransmission rate (A) meet a relationship indicated in formula (1).

The propylene polymer meeting the above requirements (a) to (c) can beobtained by using a so-called metallocene catalyst, for example.

In addition, the polypropylene resin expanded molded article of theseventh associated invention can be obtained by charging and heating ina mold, for example, the expanded particles containing the propylenepolymer having the above requirements (a) to (c) as a base resin.

In addition, the polypropylene resin expanded molded article of theseventh associated invention has the above requirement (d).

The above requirement (d) shows a relationship between the degree ofmoisture permeability and density in the above polypropylene resinexpanded molded article.

That is, in the above polypropylene resin expanded molded article, inthe case where the degree of moisture permeability measured inconformity with ATSM E-96 is defined as Y [g/m²/hr], and the density ofthe expanded molded article is defined as X [g/cm³], Y and X meet thefollowing formula (2)Y≦(43.6)·X ²−(4.5)·X+0.15   Formula (2)

In the case where the rate of water vapor transmission Y and the densityX of the above polypropylene resin expanded molded article does not meeta relationship of the above formula (2), there is a possibility that therate of water vapor transmission of the above polypropylene resinexpanded molded article is increased, and the molded article cannot beused for uses of a heat insulation material, an architectural structuralmember, a packaging material and the like.

Next, it is preferable that the above propylene polymer characterized inthat the propylene polymer further has the following requirement (e)(claim 50):

(e) an isotactic triad fraction at a propylene unit chain part which hasa head-to-tail linkage, which is measured by 13C-NMR, is 97% or more.

That is, as the above propylene polymer of the base resin, there is usedpropylene polymer in which the isotactic triad fraction (that is, a rateof three propylene unit in which propylene units are bonded with eachother in a head-to-tail manner, of arbitrary three propylene unit in thepolymer chains, and the direction of methyl branch in the propylene unitis identical) measured by 13C-NMR (nuclear magnetic resonancetechnique), is 97% or more in addition to the already describedrequirements (a) to (c).

In this case, the uniformity of foam diameter in expanded particles isfurther increased. Thus, in the case where a molded article obtainedtherefrom is used as a structural material, there can be attainedadvantageous effect that heat insulation performance or moistureproofing performance is excellent.

Hereinafter, the isotactic triad fraction is described as an mmfraction. In the case where the mm fraction is lower than 97%, themechanical properties of the above propylene polymer are lowered. Thus,there is a possibility that the mechanical properties of the abovepolypropylene resin expanded molded article are also lowered. Therefore,it is more preferable that the above mm fraction is 98% or more.

Next, it is preferable that the propylene polymer characterized in thata propylene polymer of the above core layer further has the followingrequirement (f) (claim 51):

(f) a melt flow rate is 0.5 g/10 minutes to 100 g/10 minutes.

In this case, there can be obtained advantageous effect that expandedparticles can be produced while maintaining productivity which is usefulin commercial production. Further, the above polypropylene resinexpanded molded article obtained from the expanded particles can provideadvantageous effect that its dynamic properties are excellent.

In the case where the above melt flow rate (MFR) is lower than 0.5 g per10 minutes, there is a possibility that the production efficiency of theabove expanded particles, in particular, the productivity underperforming melting and kneading process described later is lowered. Inaddition, in the case where the MFR exceeds 100 g per 10 minutes, thereis a possibility that dynamic properties such as compression strength ortensile strength of the above polypropylene resin expanded moldedarticle obtained by molding the expanded particles are lowered.Preferably, the melt flow rate is 1.0 g/10 minutes to 50 g/10 minutes.Further preferably, it is 1.0 g/10 minutes to 30 g/10 minutes.

Next, it is preferable that the above polypropylene resin expandedmolded article comprise a crystalline structure in which a peak inherentto the base resin and a peak at higher temperature than that of theinherent peak appear as endothermic peaks or a first DSC curve obtainedwhen 2 mg to 4 mg of a test specimens cut out from the abovepolypropylene resin expanded molded article are heated up to 220° C. ata rate of 10° C./minute by means of a differential scanning calorimeter(claim 52).

This phenomenon means that the above polypropylene resin expanded moldedarticle forms an inherent endothermic peak and an endothermic peak at ahigher temperature than the former on the above DSC curve.

In this case, the above propylene based resin expanded molded article ismore excellent in mechanical properties such as a compression strengthor a tensile strength.

Although a relationship between the above two endothermic peaktemperatures is not limited in particular, it is preferable that adifference between these two endothermic peak temperatures be within therange of 10° C. to 25° C. from the viewpoint of easiness of fusionduring molding and heating. The temperatures of the two endothermicpeaks vary depending on a molecular structure of a base resin, thermalhistory of a resin, amount of blowing agent, foaming temperature, andfoaming pressure or the like. In general, if foaming is performed at ahigh temperature side, the difference between the two endothermic peaksis increased.

In addition, in the seventh associated invention, other polymercomponents or additives can be mixed with the above propylene resinwhich is a base resin within the range in which advantageous effect ofthe seventh associated invention is not degraded.

For the other polymer component and additive agents, refer to the firstassociated invention.

Mixing of the above other polymer components or additives with the abovebase resin can be carried out where the polypropylene base resin is in afluid state or solid state. In general, molding and kneading is used.That is, by using a variety of kneading machines such as a roll, ascrew, a Banbury mixer, a kneader, a blender, or a mill, the above baseresin and the other component or the like are kneaded at a desiredtemperature. After kneading, the product is granulated into anappropriate size of particles suitable to production of the aboveexpanded particles.

The above resin particles are molded and kneaded in an extruder, andthen, a kneaded material is discharged out in a strand shape from a diehaving a minutely small holes. Thereafter, the resultant kneadedmaterial is cut to a specified weight or size by a cutting machine,whereby the columnar pellet shaped material can be obtained.

In general, there is no problem with production of an expanded particleobtained by heating and foaming the resin particle, when the weight ofone resin particle is 0.1 mg to 20 mg. When the weight of one resinparticle is in the range of 0.2 mg to 10 mg, and further, a deviation inweight between particles is small, expanded particles can be easilyproduced. Further, the density distribution of the obtained expandedparticles becomes small, and the filling properties of expanded resinparticles in a mold or the like is improved.

As a method of obtaining expanded particles from the above resinparticles, there can be used a method of impregnating a volatile blowingagent in resin particles fabricated as described above, followed byheating and foaming them. Specifically, for example, there can be usedmethods described in JP 1974-2183 Examined Patent Publication (Kokoku),JP 1981-1344 Examined Patent Publication (Kokoku), DE 1285722 UnexaminedPatent Publication (Kokai), and DE 2107683 Unexamined Patent Publication(Kokai).

That is, resin particles are put in a pressure vessel which can beclosed and released together with a volatile blowing agent. Then,heating is performed at or above the softening temperature, of a baseresin, and the volatile blowing agent is impregnated in the resinparticles.

Thereafter, the content within the closed vessel is discharged from theclosed vessel to a low pressure atmosphere, and then, the solid part istreated to be dried. In this manner, expanded particles are obtained.

In the above method of producing the expanded particles, a decompositiontype blowing agent can be kneaded in advance in resin particles, therebymaking it possible to obtain the above expanded particles even if theblowing agent is not fed in the pressure vessel.

As the above decomposition type blowing agent, any agent can be usedwhen it is decomposed at a foaming temperature of resin particles, andgenerates gas. Specifically, for example, there can be exemplifiedsodium bicarbonate, ammonium carbonate, an azide compound, an azocompound and the like.

In addition, during heating and foaming, it is preferable that water,alcohol or the like is used as a dispersion medium of resin particles(refer to the first associated invention)

When resin particles are discharged to a low pressure atmosphere, inorder to facilitate the discharge, it is preferable that an inorganicgas or a volatile blowing agent similar to the above is introduced fromthe outside into the closed vessel, thereby constantly maintaining theinternal pressure of the closed vessel.

Next, the molded article of the seventh associated invention can beobtained by heating the above expanded particles so that they undergosecondary foaming and fusion, followed by cooling.

In this case, a mold under various conditions is used (refer to thefirst associated invention).

Next, it is preferable that the density of the polypropylene resinexpanded molded article be 0.020 to 0.080 g/cm³ (claim 53).

In this case, the above polypropylene resin expanded molded article hasa mechanical strength and weight reduction. In addition, there can beattained advantageous effect that the molded article is excellent insurface appearance such as smoothness or glossiness. Thus, in this case,the above propylene resin expanded molded article is particularlysuitable for, for example, an architectural heat insulation material, anautomobile part, a helmet core material, a cushioning packaging materialand the like.

In the case where the density of the above polypropylene resin expandedmolded article exceeds 0.080 g/cm³, it becomes impossible tosufficiently display referred properties of an expanded particle such aslight weight, shock absorption properties, or heat insulationproperties. Further, a cost-related disadvantage may result because ofits low expanded ratio.

On the other hand, if the density is smaller than 0.020 g/cm³ there is atendency that the closed cell ratio is reduced, and there is apossibility that mechanical properties such as a bending strength or acompression strength becomes insufficient.

In addition, as use of the above polypropylene resin expanded moldedarticle, although a heat insulation material in an architectural fieldcan be exemplified as a representative one, the above polypropyleneresin expanded molded article is preferably used as an automobile'sinterior material independently or by being integrated with a variety ofskin materials.

Here, as the above automobile is interior materials, there can beexemplified a dashboard, a console box, an instrument panel, a doorpanel, a door trim, a ceiling material, an interior material of a pillarpart, a sun visor, an armrest, and headrest or the like. In addition, apart from the automobile applications, this molded article can be widelyused for a structural material such as a helmet core material, a ship orairplane, or a railway vehicle and a variety of cushioning materials.

There is no particular limitation in the above described skin materials,and for example, there can be exemplified: an elastomeric polyolefinsheet; a polystyrene resin film such as OPS (bi-axially orientedpolystyrene sheet), heat resistant OPS, or HIPS film; a polypropyleneresin film such as CPP (non-oriented polypropylene film) or OPP(bi-axially oriented polypropylene film), or a polyethylene resin film;a variety of films such as a polyethylene based resin film or apolyester base resin film; or variety of skin materials such as felt ora non-woven cloth.

The description of the seventh associated invention has now beencompleted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of polypropylene resin expanded particlesaccording to Example 21.

FIG. 2 is an illustrative view showing an entirety of a shock absorberaccording to Example 51 of the fifth associated invention.

FIG. 3 is an illustrative cross section of the shock absorber accordingto Example 51 of the fifth associated invention.

FIG. 4 is an illustrative view illustrating a stress-strain curve of theshock absorber according to Example 51 of the fifth associatedinvention.

FIG. 5 is an illustrative view showing an entirety of theshock-absorbing article according to Example 55 of the fifth associatedinvention.

FIG. 6 is an illustrative cross section of the shock-absorbing articleaccording to Example 55 of the fifth associated invention.

BEST MODE FOR CARRYING OUT THE INVENTION EXAMPLES

Now, examples of the present invention will be described below.

[Production 1 of Base Resin]

A polypropylene based polymer serving as a base resin was synthesized inaccordance with the following production examples 1 to 4.

Production Example 1

(i) Synthesis of [dimethyl sylilenebis{1,1′-(2-methyl-4-phenyl-4-hydroazulenyl)}zirconium dichloride]

All of the following reactions were carried out in an inert gasatmosphere, and a solvents were dried and purified before employing insuch reactions.

(a) Synthesis of racemic/meso mixture

2.22 g of 2-methylazulene synthesized in accordance with a methoddescribed in JP 1987-207232 Unexamined Patent Publication (Kokai) wasdissolved in 30 mL of hexane, and 15.6 ml (1.0 equivalent) ofcyclohexane-diethyl ether solution of phenyl lithium was added on asmall amount basis at 0° C.

This solution was stirred at room temperature for 1 hour, and was cooledto −78° C., and 30 mL of tetrahydrofuran was added.

Next, after adding 0.95 mL of dimethylchlorosilane, the temperature wasraised up to room temperature, and further, heating was carried out at50° C. for 90 minutes. Then, a saturated ammonium chloride aqueoussolution was added, and the organic layer was separated. Then, dryingwas carried out by using sodium sulfate, and the solvents was removedunder reduced pressure.

1.48 g of bis(1,1′-(2-mehyl-4-phenyl-1,4-dihydro azulenyl)dimethylsilanewas obtained by purifying the thus obtained crude product with silicagel column chromatography (hexane-:dichloromethane=5:1).

786 mg of the thus obtained bis(1,1′-(2-mehyl-4-phenyl-1,4-dihydroazulenyl)dimethylsilane was dissolved in 15 mL of diethyl ether; 1.98 mLof a hexane solution (1.68 mol/L) of n-butyllithium was added; thetemperature was gradually raised up to room temperature; and then, thesolution was stirred at room temperature for 12 hours. The solidobtained by removing the solvent was washed with hexane, and was driedunder vacuum

Further, 20 mL of a toluene-diethyl ether mixture (40:1) was added; 325mg of zirconium tetrachloride at −60° C.; the temperature was graduallyraised; and the mixture was stirred at room temperature for 15 minutes.

The obtained solution was condensed under reduced pressure, and hexanewas added to precipitate 150 mg of racemic/meso mixture consisting ofdimethylsilylenebis{1,1′-(2-methyl-4-phenyl-4-hydroazulenyl)}zirconium.

(b) Separation of Raceme

887 mg of the racemic/meso mixture, obtained by repeating the aboveprocedure, was put in a glass container; the mixture was dissolved in 30mL of dichloromethane and the solution was irradiated by a high voltagemercury lamp for 30 minutes. Then, dichloro methane was removed underreduced pressure, and a yellow solid was obtained.

After adding 7 mL of toluene to this solid and stirring it, and themixture was, whereby a yellow solid was separated as a sediment. Thesupernatant was removed and the a solid was dried at reduced pressure toobtain 437 mg of racemic dimethylsilylenebis

{1,1′-(2-methyl-4-phenyl-4-hydroazylenyl)}zirconium dichloride.

(ii) Synthesis of Catalyst

(a) Treatment

135 mL of desalinated water and 16 g of magnesium sulfate were put in aglass container, and was stirred to make a solution. 22.2 g ofmontmorillonite (“Kunipia-F” available from Kuminine Kogyo Co., Ltd.)was added to this solution, the temperature was raised, and the solutionwas maintained at 80° C. for 1 hour.

Next, after adding 300 mL of desalinated water, the solid component wasseparated by filtration. After adding 46 mL of desalinated water, 23.4 gof sulfuric acid, and 29.2 g of magnesium sulfate, to the solidcomponent, the temperature was raised, and the mixture was heated underreflux. Then, 200 mL of desalinated water was added, and was filtered.

Further, the procedure of addition of 400 mL of desalinated water andfiltration were carried out two times. Then, the solid was dried at 100°C., and chemically treated montmorillonite was obtained as a catalystcarrier.

(b) Preparation of Catalytic Component

After the inside of a 1 liter autoclave equipped with a stirrer wassubstituted by propylene, 230 mL of de-water heptane was introduced, andthe temperature was maintained at 40° C.

10 g of chemically treated montmorillonite as a catalytic carrier, whichwas prepared as described above, suspended in 200 mL of toluene, was putinto the autoclave.

Further, a mixture of racemicdimethylsilylenebis{1,1′-(2-methyl-4-phenyl-4-hydroazulenyl)}zirconiumdichloride (0.15 mmol), triisobutylaluminum (3 mmol) and toluene (atotal of 20 mL) were added into the autoclave.

Then, propylene was introduced for 120 minutes at a rate of 10 g/hr, andfurther, polymerization reaction was then continued for additional 120minutes. Thereafter, the solvent was removed under nitrogen atmosphereto leave behind a catalytic component. Thus, obtained catalyticcomponent contained 1.9 g of polymer per 1 g of solid component.

(iii) Polymerization of Propylene

After substituting the inside of a stirrer-equipped autoclave having 200L in internal capacity was well substituted by propylene, 45 kg ofdehydrated liquid propylene was introduced. 500 mL (0.12 mol) of hexanesolution of triisobutyl aluminum and hydrogen 3 NL) were introduced, andthe internal temperature of the autoclave was raised up to 70° C.

Then, the above solid catalyst component (1.7 g) was put into theautoclave with pressure of argon, polymerization was started, andpolymerization reaction was carried out for 3 hours.

Then, 100 mL of ethanol was put into the autoclave to stop reaction, andthe residual gas component was purged, whereby 14.1 kg of polymer wasobtained.

This polymer had the following properties: MFR=10; 99.7% ofisotactictriad fraction; melting point of 146° C. measured by a DSCtechnique (temperature was raised at a rate of 10° C. per minute from30° C.); 1.32% of position irregularity unit based on 2,1-insertion;0.08% of position irregularity unit based on 1,3-insertion.

(iv) Measurement of Water Vapor Transmission Rate

The thus obtained polymer was molded into a film of 25 micron inthickness, and water vapor transmission rate Y was measured inaccordance with a method described in JIS K7129 (this applies to thefollowing production examples). The result was 10.5 (g/m²/24 hr).

With respect to this base resin, since a melting point Tm is 146° C., Yshould be in the range of 5.8° C.≦Y≦11.8 from the above formula (1). Theabove substitute resin meets the above requirement (c), since it is inthe above range.

Production Example 2 Propylene Homopolymerization

After the inside of a stirrer-equipped 200 L autoclave was fullysubstituted with propylene, 45 kg of dehydrated liquid propylene wasintroduced. Then, 500 mL (0.12 mol) of a hexane solution of triisobutylaluminum and hydrogen (3 NL) were introduced, and the internaltemperature of the autoclave was raised up to of 40° C.

Then, the above solid catalyst component (3.0 g) was put into theautoclave with a pressure of argon, polymerization was started, andpolymerization reaction was carried out for 3 hours.

Thereafter, 100 mL of ethanol was put into a the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 4.4 kgof polymer was obtained.

The polymer had the following properties: MFR=2; 99.8% of isotactictriad fraction; melting point of 152° C. measured by the DSC technique(the temperature was raised at a rate of 10° C. per minute from 30° C.);0.89% position irregularity unit based on 2,1-insertion; and 0.005% ofposition irregularity unit based on 1,3-insertion.

Measurement of Water Vapor Transmission Rate

In addition, the water vapor transmission rate Y after molding into afilm was 9.5 (g/m²/24 hr).

With this base resin, since the melting point Tm is 152° C., Y should bein the range of 4.6≦Y≦9.8 from the above formula (1). The above baseresin meets the above requirement (c), since it is in the above range.

Production Example 3 Propylene/Ethylene Copolymerization

After the inside of a stirrer-equipped 200 L autoclave was wellsubstituted by propylene, 60 L of purified n-heptane was introduced.Then, 500 mL of a hexane solution of triisobutylaluminum (0.12 mol) wasadded, and the internal temperature of the autoclave was raised up to70° C. Thereafter, the above solid catalyst component (9.0 g) was added;a mixture gas of propylene and ethylene (propylene:ethylene=97.5:2.5 ata ratio by weight) was introduced so that the pressure is 0.7 MPa,polymerization was started, and polymerization reaction was carried outfor 3 hours under this condition.

Then, 100 mL of ethanol was put into the autoclave the reaction wasstopped; and the residual gas component was purged, whereby 9.3 kg ofpolymer was obtained. This polymer had the following properties: MFR=14;ethylene-content=2.0 wt. %; 99.2% of isotactic triad fraction; meltingpoint of 141° C.; 1.06% of position irregularity unit based on2,1-insertion; and 0.16% of position irregularity unit based on1,3-insertion.

In addition, the water vapor transmission rate Y after molding into afilm was 12.0 (g/m²/24 hr).

With respect to this base resin, since the melting point Tm is 141° C.,Y should be in the range of 6.8≦Y≦13.5. The above base resin meets theabove requirement (c), since it is in the above range.

Production Example 4 propylene/1-butene copolymerization

After the inside of a stirrer equipped 200 L autoclave was wellsubstituted by propylene, 60 L of purified n-heptane was introduced.Then, 500 mL of a hexane solution of triisobutylaluminum was added (0.12mol), and the internal temperature of the autoclave was raised up to 70°C. Thereafter, the above solid catalyst component (9.0 g) was added; amixture gas of propylene and 1-butene (propylene:1-butene=90:10) wasintroduced so that the pressure is 0.6 MPa, polymerization was started,and polymerization reaction was carried out for 3 hours under thiscondition.

Then, 100 mL of ethanol was put into the autoclave; the reaction wasstopped; and the residual gas component was purged, whereby 8.6 kg ofpolymer was obtained. This polymer had the following properties: MFR=6;1-content quantity=6.0 wt. %; melting point of 142° C.; 99.3% ofisotactic triad fraction; 1.23% of position irregularity unit based on2,1-insertion; and 0.09% of position irregularity unit based on1,3-insertion.

The water vapor transmission rate Y after molding into a film was 11.5(g/m²/24 hr).

With respect to this base resin, since the melting point Tm is 142° C.,Y should be in the range of 6.6≦Y≦13.1. The above base resin meets theabove requirement (c), since it is in the above range.

Production Example 5

After the inside of a stirrer-equipment 200 L autoclave was wellsubstituted by propylene, 60 L of the purified n-heptane was introduced,and diethyl aluminum chloride (45 g) and 11.5 g of titanium trichloridecatalyst available from Marubeni Solvay Co., Ltd. was introduced under apropylene atmosphere. Further, while a hydrogen concentration of a gasphase part is maintained to be 7.0 wt. %, propylene was introduced intothe autoclave at the autoclave internal temperature of 65° C. for 4hours at a rate of 9 kg/hr.

After stopping propylene introduction, reaction was further continuedfor 1 hour, 100 mL of butanol was added to the reaction mixture to stopreaction, and the residual gas component was purged, whereby 30 kg ofpolymer was obtained.

This polymer had the following properties: MFR=10; melting point of 160°C.; 97% of isotactic triad fraction; 0% of position irregularity unitbased on 2,1-insertion; and 0% of position irregularity unit based on1,3-insertion.

The water vapor transmission rate Y after molded as a film was 10.0(g/m²/24 hr).

Since the melting point Tm of this base resin is 160° C., Y should be inthe range of 3.0≦Y≦7.2 from the above formula (1). However, the resultfor the above base resin is not in the above range.

That is, this resin fails to meet the requirement (c) of claim 1 of thefirst associated invention.

Production Example 6

After the inside of the stirrer-equipped 200 L autoclave was wellsubstituted by propylene, 60 L of purified n-heptane was introduced.Then, diethyl aluminum chloride (40 g) and 7.5 g of titanium trichloridecatalyst available from Marubeni Solvay Co., Ltd. was introduced under apropylene atmosphere. Further, while the hydrogen concentration of a gasphase part is maintained at 7.0 wt. %, in the auto clave at 60° C., amixture gas of propylene and ethylene (propylene:ethylene=97.5:2.5 inratio by weight) was introduced so that the pressure is 0.7 MPa.

After stopping mixture gas introduction, reaction was further continuedfor 1 hour; 100 mL of butanol was added to the reaction mixture to stopreaction; and the residual gas component was purged, whereby 32 kg ofpolymer was obtained.

This polymer had the following properties: MFR=12; melting point of 146°C.; 96% of isotactic triad fraction; 0% of position irregularity unitbased on 2,1-insertion; and 0% of position irregularity unit based on1,3-insertion.

The water vapor transmission rate Y after molded as a film was 15.0(g/m²/24 hr).

Since the melting point Tm of this base resin is 146° C., Y should be inthe range of 5.8≦Y≦11.8 from the above formula (1) However, the abovebase resin is not in the above range.

That is, this resin fails to meet the requirement (c) of claim 1 of thefirst associated invention.

Now, a description will be given with respect to Examples in whichpolypropylene based resin foam particles are produced by using the baseresin obtained by the above described Production Examples 1 to 6.

Example 1

Two antioxidants, 0.05 wt. % of (trade name “Yoshinox BHT” availablefrom Yoshitomi Pharmaceuticals, Co., Ltd and 0.10 wt. % of trade name“Irganox 1010” available from Ciba-Geigy Co., Ltd.) were added to apropylene homopolymer obtained in Production Example 1 as a base resin,and the mixture was extruded into the form of strands of 1 mm indiameter using a single axis extruder of 65 mm in diameter. Aftercooling in water, the strands were cut into pellets having length of 2mm.

1,000 g of this pellet was put into a 5 liter autoclave, together with2,500 g of water, 200 g of calcium tertiary phosphate triphosphate and0.2 g of sodium dodecyl benzene sulfonate. Further, 120 g of isobutanewas added, and the temperature was raised up to 135° C. over 60 minutes.Then, the reaction mixture was maintained at this temperature for 30minutes.

Then, while supplying nitrogen gas into the autoclave so as to maintainthe pressure at 2.3 MPa, a valve at the bottom part of the autoclave wasopened. Then, the contents were discharged into an atmosphere of air.

After drying the expanded particles obtained by the above operation, thebulk density was measured, the measurement was 32 g/L. In addition, theaverage size of the foam of the particles were 280 micron in diameter,which was very uniform.

Then, the thus obtained polypropylene based expanded particles weresequentially charged under compression into an aluminum mold from ahopper by using compressed air. Thereafter, heating and molding werecarried out by introducing a steam of 0.25 MPa gauge pressure into thechamber of the mold, and a molded article was obtained.

The molded article had 0.058 g/cm³ of density, a dimension of 300 mmvertical, 300 mm horizontal, and 50 mm in thickness. The molded articlehad little voids on the surface, having superior surface appearance freeof irregularities. In addition, when the degree of fusion of a crosssection was measured by breaking the article at the center of it, theresult was 80%.

In addition, a test specimen of 50 mm vertical, 50 mm horizontal, and 25mm in thickness was prepared from another molded article molded underthe same molding condition, and a compression test was carried out inconformance with JIS K6767. As a result, the stress during 50%compression was 7.2 kg/cm². Further, using a testing specimen of thesame size, when a permanent set after compression was measured by themethod described in JIS K6767, the measurement was 11%.

The results are shown in Table 1. TABLE 1 Comparative ComparativeExample 1 Example 2 Example 3 Example 4 Example 5 Example 1 Example 2base production example production production production productionproduction production production resin example 1 example 2 example 3example 4 example 4 example 5 example 6 MFR (g/10 minutes) 10 2 14 6 610 12 comonomer — — ethylene 1-butene 1-butene — ethylene contents ofcomonomer — — 2.0 6 6 — 2.6 (wt %) melting point (° C.) 146 152 141 142142 160 146 water vapor transmission rate 10.5 9.5 12.0 11.5 11.5 10.015.0 (g/m²/24 hr) [mm] fraction (%) 99.7 99.8 99.2 99.3 99.3 97 96 [2,1] insertion (%) 1.32 0.89 1.06 1.23 1.23 0 0 [1, 3] insertion (%) 0.080.005 0.16 0.09 0.09 0 0 foaming temperature (° C.) 135 140 130 130 132150 135 bulk density of expanded 32 29 30 27 20 0.46 39 particle (g/L)condition of foam average average 240μ; average 250μ; average 230μ;average 300μ; average 200μ; average 180μ; 280μ; well uniformed welluniformed well uniformed well uniformed widely varied widely varied welluniformed particle density (g/L) 58 55 56 58 35 67 61 fusion (%) 90 8595 95 95 40 60 appearance of molded article ◯ ◯ ◯ ◯ ◯ X X˜Δ compressiontest (kg/cm²) 7.2 8.0 6.9 7.5 7.4 4.5 5.3 permanent set aftercompression (%) 11 12 9 10 9 16 15Notes1) In the table, “—” of “comonomer” and “content of comonomer” sectionmeans polymerisation is conducted without adjunction of comonomer.2) Appearance of molded article. ◯: Excellent Δ: Acceptable X: Poor

(Examples 2 to 5) and (Comparative Examples 1 and 2)

Testing was carried out in the same manner as in Example 1 except thatbase resins described in Table 1 (the above production examples 1 to 6)were used.

The results are shown in Table 1.

As shown by the data in Table 1, in the case where there is employed abase resin which fails to meet the above requirement (c) derived fromthe above production examples 5 and 6 (in Comparative Examples 1 and 2),the obtained polypropylene based resin expanded particles had foams withwide distribution in the size. In addition, the molded article molded byemploying the polypropylene based resin expanded particles is low indegree of internal fusion, and further, the surface appearance of themolded article was poor. In addition, the mechanical properties wereinsufficient.

In contrast, in Examples 1 to 5 according to the present invention, itis evident that foams of the polypropylene resin expanded particles arevery uniform, the degree of fusion of the molded article using theparticles is also high, and the surface appearance is excellent. Inaddition, with respect to the mechanical properties as well, thecompression strength was high, and the permanent set after compressionwas small.

Now, Examples of the second associated invention will be described here.

[Production 1 of Base Resin]

A propylene polymer as a base resin forming a core layer was synthesizedin accordance with the following Production Examples 1 to 4.

Production Example 1

(i) Synthesis of [dimethyl sylilenebis{1,1′-(2-methyl-4-phenyl-4-hydroazulenyl)}zirconium dichloride]

All of the following reactions were performed in an inert gasatmosphere, and solvents were dried and purified before using in suchreactions.

(a) Synthesis of racemic/meso mixture

(b) Separation of Racemic isomer

(ii) Synthesis of Catalyst

(a) Treatment of Catalyst Carrier

(b) Preparation of Catalyst Component

The above description is similar to that of Production Example 1 of thefirst associated invention.

(iii) Polymerization of Propylene

After substituting the inside of a stirrer-equipped 200 L autoclave withpropylene, 45 kg of dehydrated liquid propylene was introduced.

Then, 500 mL (0.12 mol) of a hexane solution of triisobutyl aluminum andhydrogen (3 NL) were introduced, and the internal temperature of theautoclave was raised up to 70° C.

Then, the above solid catalyst component (1.7 g) was put into theautoclave with pressure of argon, polymerization was started, andpolymerization reaction was performed for 3 hours.

Thereafter, 100 mL of ethanol was put into the reaction mixture, thereaction was stopped, and the residual gas component was purged, whereby14.1 kg of polymer was obtained as a propylene polymer for a core layer.

This polymer had the following properties: MFR=10; 99.7% of isotactictriad fraction; a melting point of 146° C. measured by the DSC technique(the temperature was raised at a rate of 10° C./minute from 30° C.);1.32% of position irregularity unit based on 2,1-insertion; 0.08% ofposition irregularity based on 1,3-insertion.

(iv) Measurement of Water Vapor Transmission Rate

The above obtained polymer was molded in film having a thickness of 25micron, and water vapor transmission rate Y was measured in accordancewith a method described in JIS K7129 (this applies to the followingproduction examples). The result was 10.5 (g/m²/24 hr).

In this propylene polymer, the melting point Tm was 146° C. Thus, fromthe above formula (1), Y should be in the range of 5.8≦Y≦11.8. Y was inthis range, and thus, met the above requirement (c) of the secondassociated invention.

Production Example 2 Propylene Homopolymerization

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 45 kg of dehydrated liquid propylene wasintroduced. Then, 500 mL (0.12 mol) of a hexane solution of triisobutylaluminum and hydrogen (3 NL) were introduced, and the internaltemperature of the autoclave was raised up to 40° C.

Thereafter, the above solid catalyst component (3.0 g) was put into theautoclave with pressure of argon, polymerization was started, andpolymerization reaction was performed for 3 hours.

Thereafter, 100 mL of ethanol was put into the reaction mixture,reaction was stopped, and the residual gas component was purged, whereby4.4 kg of polymer was obtained as a propylene polymer for a core layer.

This polymer had the following properties: MFR=2; 99.8% of isotactictriad fraction; a melting point of 152° C. measured by the DSC technique(the temperature was raised at a rate of 10° C./minute from 30° C.);0.89% of position irregularity unit based on 2,1-insertion; 0.005% ofposition irregularity based on 1,3-insertion.

Measurement of Water Vapor Transmission Rate

In addition, the water vapor transmission rate Y after molded in filmwas 9.5 (g/m²/24 hr).

In this propylene polymer, the melting point Tm is 152° C. Thus, fromthe above formula (1), Y should be in the range of 4.6≦Y≦9.8. Y was inthis range, and thus, met the above requirement (c) of the secondassociated invention.

Production Example 3 Propylene/Ethylene Copolymerization

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L purified n-heptane was introduced.Then, 500 mL (0.12 mol) of a hexane solution of triisobutyl aluminum wasintroduced, and the internal temperature of the autoclave was raised upto 70° C.

Thereafter, the above solid catalyst component (9.0 g) was added, amixture gas of propylene and ethylene (propylene ethylene=97.5:2.5 inratio by weight) was introduced so that the pressure is 0.7 MPa,polymerization was started, and polymerization reaction was performedunder this condition for 3 hours.

Thereafter, 100 mL of ethanol was put into the reaction mixture,reaction was stopped, the residual gas component was purged, whereby 9.3kg of polymer was obtained as a propylene polymer for a core layer. Thispolymer had the following properties: MFR=14; ethylene content=2.0% byweight, 99.2% of isotactic triad fraction, a melting point of 141° C.,1.06% of position irregularity unit based on 2,1-insertion, 0.16% ofposition irregularity unit based on 1,3-insertion.

In addition, the water vapor transmission rate Y after molded in filmwas 12.0 (g/m²/24 hr).

In this propylene polymer, the melting point Tm was 141° C. Thus, fromthe above formula (1), Y should be in the range of 6.8≦Y≦13.5. Y was inthat range, and thus, met the above requirement (c) of the secondassociated invention.

Production Example 4 Propylene/1-Butene Copolymerization

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was introduced;500 mL of a hexane solution of triisobutyl aluminum was added; and theinternal temperature of the autoclave was raised up to 70° C.Thereafter, the above solid catalyst component (9.0 g) was added; amixture gas of propylene and 1-butene (propylene:1-butene=90:10) wasintroduced so that the pressure is 0.6 MPa, and polymerization reactionwas performed for 3 hours under this condition.

Thereafter, 100 mL of ethanol is put into the reaction mixture; reactionwas stopped; and the residual gas component was purged, whereby 8.6 kgof polymer was obtained as a propylene polymer for a core layer. Thispolymer had the following properties: MFR=6,1-butene content=6.0% byweight; a melting point of 142° C.; 99.3% of isotactic triad fraction;1.23% of position irregularity unit based on 2,1-insertion; 0.09% ofposition irregularity unit based on 1,3-insertion.

The water vapor transmission rate Y after molded in film was 11.5(g/m²/24 hr).

In this propylene polymer, the melting point Tm was 142° C. Thus, fromthe above formula (1), Y should be in the range of 6.6≦Y≦13.1. Y was inthat range, and thus met the above requirement (c) of the secondassociated invention.

Production Example 5

After the inside of a 200 L stirrer-equipped was thoroughly substitutedwith propylene, 60 L of purified n-heptane was introduced; diethylaluminum chloride (45 g) and 11.5 g of titanium trichloride catalystavailable from Marubeni Solvay Co., Ltd. were introduced under apropylene atmosphere. Further, while the hydrogen concentration of a gasphase part was maintained at 7.0% by volume, propylene was introducedinto the autoclave over 4 hours at an autoclave internal temperature of65° C. and at a rate of 9 kg/hour.

After propylene introduction was stopped, 1-hour reaction was furthercontinued. 100 mL of butanol was added in the autoclave and the reactionwas stopped; and the residual gas component was purged, whereby 30 kg ofpolymer was obtained as a propylene polymer for a core layer.

This polymer had the following properties: MFR=10; a melting point of160° C.; 97% of isotactic triad fraction; 0% of position irregularityunit based on 2,1-insertion; 0% of position irregularity unit based on1,3-insertion.

The water vapor transmission rate Y after molded in film was 10.0(g/m²/24 hr).

In this propylene polymer, a melting point Tm was 160° C. Thus, from theabove formula (1), Y should be in the range of 3.0≦Y≦7.2, and however,was not in that range.

That is, this polymer did not meet the requirement (c) of the firstinvention of the second associated invention (claim 6).

Production Example 6

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was introduced;diethyl aluminum chloride (40 g) and 7.5 g of titanium trichloridecatalyst available from Marubeni Solvay Co., Ltd. were introduced undera propylene atmosphere. Further, while the hydrogen concentration of agas phase part was maintained at 7.0% by volume, a mixture gas ofpropylene and ethylene (propylene:ethylene=97.5:2.5 in ratio by weight)was introduced into the autoclave at 60° C. so that the pressure is 0.7MPa.

After mixture gas introduction was stopped, the reaction was furthercontinued for 1 hour; 100 mL of butanol was added in the autoclave andthe reaction was stopped; and the residual gas component was purged,whereby 32 kg of polymer was obtained as a propylene polymer for a corelayer.

This polymer had the following properties: MFR=12; a melting point of146° C.; 96% of isotactic triad fraction; 0% of position irregularityunit based on 2,1-insertion; 0% of position irregularity unit based on1,3-insertion.

The water vapor transmission rate Y after molded in film was 15.0(g/m²/24 hr).

In this propylene polymer, a melting point Tm was 146° C. Thus, from theabove formula (1), Y should be in the range of 5.8≦Y≦11.8, and however,was not in that range.

That, this polymer did not meet the requirement (c) of the firstinvention of the second associated invention (claim 6).

Next, a description will be given with respect to Examples in whichpolypropylene resin expanded particles were produced by using apropylene polymer obtained in accordance with Production Examples 1 to 6described above.

In the following Examples, the properties were obtained as follows.

<Melting Point>; By using a differential scanning calorimeter (DSC), atemperature of 3 mg to 5 mg of sample consisting of a propylene polymerobtained in accordance with each of the above described productionexamples 1 to 6 or a resin of a coat layer described in Tables 1 and 2described later, was raised from 20° C. to 220° C. at a rate of 10°C./minute. Then, the temperature was reduced to 20° C. at a rate of 10°C./minute, and further, a melting point was defined with a peaktemperature on an endothermic curve obtained by raising a temperature to220° C. at a rate of 10° C./minute again.

<Fusion Test>; Propylene resin expanded particles comprising of a corelayer and a coat layer, described later, was fabricated by using theabove propylene polymer. Next, the particles were heated and molded byintroducing a high pressure steam after charging the particles into amold by compression filling; a molded article was produced. Then, thethus produced molded article was cut out, and a test specimen of 200 mmin length, 30 mm in width, and 12.5 mm in thickness was fabricated.

This test specimen was bent up to 90 degrees along the periphery of acylinder of 50 mm in diameter, and was judged based on the followingcriteria.

-   O: 80% or more out of total number of test specimens was not broken.-   X: More than 20% out of total number of test specimens was broken.    <Heat Resistance Test>; The degree of dimensional change after    heating at 110° C. was measured in conformance with JIS K6767, and    was judged based on the following criteria

This test specimen was fabricated in accordance with procedures similarto those of the method which was already described in the≦FusionTest>section.

-   O: The degree of dimensional change after heating was lower than 3%.-   Δ: The degree of dimensional change after heating was 3% to 6%-   X: The degree of dimensional change after heating exceeds 6%

Example 21

By using a single screw extruder of 65 mm in internal diameter,antioxidants (0.05% by weight of trade name “Yoshinox BHT” availablefrom Yoshitomi Pharmaceuticals, Co., Ltd.) and 0.10% by weight of tradename “Irganox 1010” available from Ciba Geigy Co., Ltd. were added tothe propylene homopolymer obtained in Production Example 1, and waskneaded, and then, linear polyethylene with a low density of 0.920 waskneaded by using a single screw extruder of 30 mm in internal diameter.

Next, from a die having a die orifice of 1.5 mm in diameter, the abovepropylene homopolymer was applied as a material for a core layer, linearlow density polyethylene of 0.92 g/cm³ of density and 121° C. in meltingpoint was applied as a material for a coat layer, and these layers wereextruded in a strand shape.

Further, this strand was cooled through a water tank; the cooled strandwas cut so that the weight of one piece is 1.0 mg, and a fine granulepellet was obtained as resin particles. When these resin particles wereobserved by a phase contrast microscope, a propylene polymer as a corelayer was coated with the linear low density polyethylene with thicknessof 30 micron as a coat layer.

Next, in order to obtain the above resin particles as expandedparticles, 1000 g of the above fine granule pellet was put into a 5liter autoclave, together with 2500 g of water, 200 g of 10% waterdispersion of calcium tertiary phosphate, and 30 g of sodiumdodecylbenzenesulfonate (2% aqueous solution). Further, 200 g ofisobutane was added, the temperature was raised up to 135° C. over 60minutes, and the reaction mixture was maintained at this temperature for30 minutes.

Then, while supplying nitrogen gas into the autoclave so as to maintainthe pressure at 2.3 MPa, a valve at the bottom part of the autoclave wasopened. Then, the contents were discharged into the atmosphere of air,and foaming was performed.

After drying the expanded particles obtained by the above operation, thebulk density of polypropylene resin expanded particles was measured; theresult was 24 kg/m³. In addition, the average size of the foam ofpolypropylene resin expanded particles was 340 micron, which was veryuniform.

As shown in FIG. 1, the above described polypropylene resin expandedparticle 1 was a columnar fine granule pellet consisting of the abovecore layer 11 and the above coat layer 12 covering its outer periphery.

Next, the above obtained propylene resin expanded particles weresequentially charged under compression into an aluminum mold from ahopper by using compressed air. Thereafter, heating and molding werecarried out by introducing a steam of 0.15 MPa (gauge pressure) into thechamber of the mold, and a molded article was obtained.

The molded article had 45 kg/m³ of density, a dimension of 300 mmvertical, 300 mm horizontal, and 50 mm in thickness. The molded articlehad little voids on the surface, having superior surface appearance. Inaddition, when the degree of fusion of a cross section by breaking thearticle at the center of it was measured, the result was 80%.

In addition, after a test specimen of a dimension of 50 mm vertical, 50mm horizontal, and 25 mm in thickness was prepared from another moldedarticle molded under the same molding condition, and a compression testwas carried out in conformance with JIS K7220. As a result, the stressat 50% compression was 0.52 MPa. Further, using a testing specimen ofthe same size, when a permanent set after compression was measured bythe method described in JIS K6767, the result was 11%

The result is shown in Table 2.

(Examples 22 to 28) and (Comparative Examples 21 to 23)

The above Examples and Comparative Examples were carried out in the samemanner as in Example 21 except that a base resin forming a core layerdescribed in each of the above Production Examples 1 to 6was used, and aresin forming a coat layer described in each of Tables 2 to 4 was used.

The results are shown in Tables 2 to 4.

As shown by the data in Tables 2 to 4, in the case of using a base resinwhich fails to meet the above requirement (c) obtained from the aboveProduction Examples 5 and 6 (Comparative Examples 21, 22 and 23), theobtained polypropylene resin expanded particles had foamed with widedistribution in the size.

In addition, the molded article molded by using the polypropylene resinexpanded particles was low in degree of internal fusion, and inaddition, the surface appearance of the molded article was poor.Further, the mechanical properties were insufficient.

In contrast, in Examples 21 to 28 according to the present invention, itis evident that the foams of polypropylene resin expanded particles werevery uniform; the degree of fusion of the molded article using theparticles is also high; and further, the surface appearance isexcellent. Further, with respect to the mechanical properties, thecompression strength is high, the permanent set after compression issmall, and further, heat resistance is excellent. TABLE 2 ExampleExample 21 Example 22 Example 23 Example 24 production example of resinfor core layer production production production production example 1example 1 example 1 example 2 polypropylene core layer MFR (g/10minutes) 10 10 10 2 resin expanded melting point (° C.) 146 146 146 152particle water vapor transmission rate (g/m²/24 hr) 10.5 10.5 10.5 9.5[mm] fraction (%) 99.7 99.7 99.7 99.8 [2,1] insertion (%) 1.32 1.32 1.320.89 [1,3] insertion (%) 0.08 0.08 0.08 0.005 coat layer resin for coatlayer LLDPE LLDPE HIPS LLDPE density (g/cm³) 0.92 0.92 1.05 0.92 meltingpoint (° C.) 121 121 none 121 thickness of coat layer (μ) 30 70 30 30weight of composite particle (mg) 1.0 1.0 1.0 1.0 foaming temperature (°C.) 135 135 135 140 average bulk density of expanded particle (kg/m³) 2525 25 25 average size of foam (μ) 340 300 340 340 condition of foamhighly uniform highly uniform highly uniform highly uniform expandedsteam pressure for molding (MPa) 0.15 0.15 0.12 0.15 molded articledensity of molded article (kg/m³) 45 45 45 45 appearance of moldedarticle ◯ ◯ ◯ ◯ mold-to-part contraction (%) 1.6 1.9 1.6 1.7 fusion test◯ ◯ ◯ ◯ compression test (MPa) 0.52 0.50 0.55 0.58 permanent set aftercompression (%) 11 11 12 11 heat resistance test ◯ ◯ ◯ ◯LLDPE: Linear Low Density PolyethyleneHIPS: HIPS grade name “HT60” available from A and M Polystyrene Co.,Ltd.

TABLE 3 Example Comparative Comparative Example 25 Example 26 Example 21Example 22 production example of resin for core layer productionproduction production production example 3 example 4 example 5 example 6polypropylene core layer MFR (g/10 minutes) 10 6 10 2 resin expandedmelting point (° C.) 141 142 160 146 particle water vapor transmissionrate (g/m²/24 hr) 12.0 11.5 10.0 15.0 [mm] fraction (%) 99.2 99.3 97.096.0 [2, 1] insertion (%) 1.06 1.23 0 0 [1, 3] insertion (%) 0.16 0.09 00 coat layer resin for coat layer LLDPE LLDPE LLDPE LLDPE density(g/cm³) 0.92 0.92 0.92 0.92 melting point (° C.) 121 121 121 121thickness of coat layer (μ) 30 30 30 30 weight of composite particle(mg) 1.0 1.0 1.0 1.0 average bulk density of expanded particle (kg/m³)19 20 24 24 average size of foam (μ) 320 300 120 260 condition of foamhighly uniform highly uniform widely varied widely varied expanded steampressure for molding (MPa) 0.15 0.15 0.15 0.15 molded article density ofmolded article (kg/m³) 45 45 45 45 appearance of molded article ◯ ◯ X Xmold-to-part contraction (%) 1.6 1.6 2.2 2.3 fusion test ◯ ◯ X Xcompression test (MPa) 0.47 0.48 0.51 0.44 permanent set aftercompression (%) 11 11 17 16 heat resistance test ◯ ◯ Δ ΔLLDPE: Linear Low Density Polyethylene

TABLE 4 Comparative Example Example 27 Example 28 Example 23 productionexample production production production of resin for core layer example1 example 1 example 1 polypropylene resin for composition LLDPE2composition resin expanded coat layer A B particle thickness 30 30 30 ofcoat layer (μ) weight of 1.0 1.0 1.0 composite particle (mg) averagebulk 25 24 21 density of expanded particle (kg/m³) expanded steam 0.170.1 0.17 molded article pressure for molding (MPa) density of 40 40 40molded article (kg/m³) mold-to-part 1.6 1.6 1.6 contraction (%) fusiontest ◯ ◯ X compression 0.47 0.45 could not be test (MPa) performed heat◯ ◯ could not be resistance performed testcomposition A:(1) Linear low density polyethylene (density 0.920 and melting point120° C.) [100 parts by weight](2) Propylene polymer obtained in Production Example 1 [20 parts byweight]composition B:(1) Linear low density polyethylene (density 0.920 and melting point120° C.) [100 parts by weight](2) Propylene polymer obtained in Production Example 1 [150 parts byweight]LLDPE2: Linear Low Density Polyethylene (density 0.907 and melting point100° C.)

Now, Examples of the third associated invention will be described here.

[Production of Propylene Polymer]

First, propylene polymers [A] and [B] constituting a polypropylene resincomposition were synthesized by any of the methods shown in thefollowing Production Examples 1 to 6.

Production Example 1

(i) Synthesis of[dimethylsilylenebis{1,1′-(2-methyl-4-phenyl-4-hydroazulenyl)}zirconiumdichloride]

All of the following reactions were performed in an inert gasatmosphere, and solvents were dried and purified before using in suchreactions.

(a) Synthesis of racemic/meso mixture

(b) Separation of racemic isomer

(ii) Synthesis of Catalyst

(a) Treatment of Catalyst Carrier

(b) Preparation of Catalyst Component

The above description is similar to that of Production Example 1 of thefirst associated invention.

(iii) Polymerization of Propylene (Production of Propylene Polymer A)

After substituting the inside of a stirrer-equipped 200 L autoclave waswell substituted with propylene, 45 kg of dehydrated liquid propylenewas introduced. Then, 500 ml (0.12 mol) of a hexane solution oftriisobutyl aluminum and hydrogen (3 NL) were introduced, and theinternal temperature of the autoclave was raised up to 70° C.

Thereafter, the above solid catalyst component (1.7 g) was put into theautoclave under pressure of argon, polymerization was started, andpolymerization reaction was performed for 3 hours.

Thereafter, 100 ml of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 14.1 kgof polymer was obtained.

This polymer is 100 mol % in structural unit derived from propylene,i.e., a propylene homopolymer. This polymer meets the above requirement(a) of the third associated invention.

In addition, this polymer had the following properties: MFR (melt flowrate)=10 g/10 minutes; 99.7% of isotactic triad fraction; a meltingpoint of 146° C. measured by the DSC technique (the temperature wasraised at a rate of 10° C./minute from 30° C.) The polymer met the aboverequirements (d) and (e) of the third associated invention. Further, acontent of position irregularity unit based on 2,1-insertion was 1.32%;a content of position irregularity based on 1,3-insertion was 0.08%; andthe above requirement (b) of the third associated invention was met.

Hereinafter, the thus obtained polypropylene polymer is referred to as“polymer 1”.

(iv) Measurement of Water Vapor Transmission Rate

The above obtained polymer 1 was molded into a film of 25 micron inthickness, and the water vapor transmission rate Y was measured inaccordance with the method described in JIS K 7129 (this applies to thefollowing production examples). The result was 10.5 (g/m²/24 hr).

In polymer 1, as described above, the melting point Tm was 146° C. Fromthe above formula (1), Y should be in the range of 5.8≦Y≦11.8. Y was inthat range, and met the above requirement (c) of the third associatedinvention.

Production Example 2 Production of Propylene Polymer [A]; PropyleneHomopolymerization

After a stirrer-equipped 200 L autoclave was thoroughly substituted withpropylene, 45 kg of dehydrated liquid propylene was introduced. Then,500 ml (0.12 mol) of a hexane solution of triisobutyl aluminum andhydrogen (3 NL) were introduced, and the internal temperature of theautoclave was raised up to 40° C.

Thereafter, the above solid catalyst component (3.0 g) was put into theautoclave with pressure of argon, polymerization was started, andpolymerization reaction was performed for 3 hours.

Thereafter, 100 ml of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 4.4 kgof a polymer was obtained.

This polymer is 100 mol % in structural unit derived from propylene,i.e., a propylene homopolymer. This polymer meets the above requirement(a) of the third associated invention.

In addition, this polymer had the following properties: MFR=2; 99.8% ofisotactic triad fraction; a melting point of 152° C. measured by the DSCtechnique (the temperature was raised at a rate of 10° C./minute from30° C.). The polymer met the above requirements (d) and (e) of the thirdassociated invention. Further, a content of position irregularity unitbased on 2,1-insertion was 0.89%; a content of position irregularityunit based on 1,3-insertion was 0.005%; and the above requirement (b) ofthe third associated invention was met.

Hereinafter, the thus obtained polypropylene polymer is referred to as¢polymer 2”.

Measurement of Water Vapor Transmission Rate

In addition, with respect to the polymer 2, when the water vaportransmission rate Y when the polymer is molded into a film wasinvestigated as in the above polymer 1, the transparency was 9.5(g/m²/24 hr).

In polymer 2, as described above, the melting point Tm was 152° C. Thus,from the above formula (1), Y should be in the range of 4.6≦Y≦9.8. Y wasin that range, and thus, met the above requirement (c) of the thirdassociated invention.

Production Example 3 Production of Propylene Polymer [A] andPropylene/Ethylene Copolymerization

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted by propylene, 60 L of purified n-heptane was introduced. 500ml of a hexane solution of triisobutyl aluminum (0.12 mol) was added,and the internal temperature of the autoclave was raised up to 70° C.Thereafter, the above solid catalyst component (9.0 g) was added; amixture gas of propylene and ethylene (propylene:ethylene=97.5:2.5 at aratio by weight) was introduced so that the pressure is 0.7 MPa;polymerization was started and polymerization reaction was performed for3 hours under this condition.

Thereafter, 100 ml of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 9.3 kgof polymer was obtained.

In this polymer, the content of the structural unit derived frompropylene was 97.0 mol %, and the content of the structural unit derivedfrom ethylene was 3.0 mol %. These values met the above requirement (a)of the third associated invention.

In addition, this polymer had the following properties: MFR=14; ethylenecontent=2.0% by weight; 99.2% of isotactic triad fraction; a meltingpoint of 141° C. measured by the DSC technique (the temperature wasraised at a rate of 10° C./minute from 30° C.) The polymer met the aboverequirements (d) and (e) of the third associated invention. Further, thecontent of position irregularity unit based on 2,1-insertion was 1.06%;the content of position irregularity unit based on 1,3-insertion was0.16%; and the above requirement (b) of the third associated inventionwas met.

Hereinafter, the thus obtained polypropylene polymer is referred to as“polymer 3”.

In addition, with respect to the polymer 3, when the water vaportransmission rate Y after molding into a film was investigated as in theabove polymers 1 and 2, the rate was 12.0 (g/m²/24 hr).

In polymer 3, as described above, the melting point Tm was 141° C. Thus,from the above formula (1), Y should be in the range of 6.8≦Y≦13.5. Ywas in that range, and thus, met the above requirement (c) of the thirdassociated invention.

Production Example 4 Production of Propylene Polymer [A] andPropylene/1-Butene Copolymerization

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted by propylene, 60 L of purified n-heptane was introduced. 500ml of a hexane solution of triisobutyl aluminum (0.12 mol) was added,and the internal temperature of the autoclave was raised up to 70° C.Thereafter, the above solid catalyst component (9.0 g) was added; amixture gas of propylene and 1-butene (propylene:1-butene=90:10 ratio byweight) was introduced so that the pressure is 0.6 MPa; polymerizationwas started; and polymerization reaction was performed for 3 hours underthis condition.

Thereafter, 100 ml of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 8.6 kgof a polymer was obtained.

In this polymer, the content of the structural unit derived frompropylene 95.4 mol %, and the contentof the structural unit derived from1-butene was 4.6 mol %. These values met the above requirement (a) ofthe third associated invention.

In addition, this polymer had the following properties: MFR=6; 1-butenecontent=6.0% by weight; a melting point of 142° C. measured by the DSCtechnique (the temperature was raised at a rate of 10° C./minute from30° C.); 99.3% of isotactic triad fraction. The polymer meets the aboverequirements (d) and (e) of the third associated invention. Further, acontent of position irregularity unit based on 2,1-insertion was 1.23%;a content of position irregularity unit based on 1,3-insertion was0.09%; and the above requirement (b) of the third associated inventionwas met.

Hereinafter, the thus obtained polypropylene polymer is referred to as“polymer 4”.

In addition, with respect to the polymer 4, when the water vaportransmission rate Y when the polymer is molded into a film wasinvestigated as in the above polymers 1 to 3, the transparency was 11.5(g/m²/24 hr).

In polymer 4, as described above, the melting point Tm was 142° C. Thus,from the above formula (1), Y should be in the range of 6.6≦Y≦13.1. Ywas in that range, and thus, met the above requirement (c) of the thirdassociated invention.

Production Example 5 Production of Propylene Polymer [B] and PropyleneHomopolymerization

After the inside of a stirrer-equipped 200 L autoclave thoroughly wellsubstituted by propylene, 60 L of purified n-heptane was introduced, anddiethyl aluminum chloride (45 g) and 11.5 g of a titanium trichloridecatalyst available from Marubeni Solvay Co., Ltd. was introduced under apropylene atmosphere. Further, while the hydrogen concentration of a gasphase part was maintained at 7.0 vol %, propylene was introduced in theautoclave at the autoclave internal temperature of 60° C. over 4 hoursat a rate of 9 kg/hour.

After stopping propylene introduction, the reaction was furthercontinued for 1 hour; 100 ml of butanol was added to the reactionmixture to stop reaction, and the residual gas component was purged,whereby 26 kg of polymer was obtained. The thus obtained polymer isreferred to as “polymer 5”.

This polymer is 100 mol % in structural unit derived from propylene,that is, is a propylene homopolymer. This polymer met the aboverequirement (a) of the third associated invention.

This polymer had the following properties: MFR=7; a melting point of165° C.; 97.6% of isotactic triad fraction; 0% of position irregularityunit based on 2,1-insertion; 0% of position irregularity unit based on1,3-insertion.

That is, this polymer did not meet the above requirement (b) of thethird associated invention.

With respect to polymer 5, as in the above polymers 1 to 4, when thewater vapor transmission rate Y after molded into a film wasinvestigated, the result was 7.8 (g/m²/24 hr).

In polymer 5, as described above, the melting point Tm was 165° C., andthus, Y should be in the range of 2.0≦Y≦5.6. However, Y was not in thatrange.

That is, polymer 5 did not meet the above requirement (c) of the thirdassociated invention.

Production Example 6 (Production of Propylene Polymer [B] andPropylene/Ethylene Copolymerization

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted by propylene, 60 L of purified n-heptane was introduced,then diethylaluminumchloride (40 g) and 7.5 g of a titanium trichloridecatalyst available from Marubeni Solvay Co., Ltd. was introduced under apropylene atmosphere. Further, while the hydrogen concentration of a gasphase part was maintained at 7.0 vol %, amixture gas of propylene andethylene (propylene:ethylene=97.5:2.5 at ratio by weight) was introducedso that the pressure is 0.7 MPa at 60° C.

After stopping mixture gas introduction, reaction was further continuedfor 1 hour; 100 ml of butanol was added to the reaction mixture to stopthe reaction was; and the residual gas component was purged, whereby 32kg of a polymer was obtained. The thus obtained polymer is referred toas “polymer 6”.

This polymer had 96.1 mol % of structural unit derived from propylene,and 3.9 mol % of structural unit derived from ethylene. This polymer metthe above requirement (a) of the third associated invention

This polymer 6 had the following properties: MFR=12; a melting point of146° C.; 96% of isotactic triad fraction; 0% of position irregularityunit based on 2,1-insertion; 0% of position irregularity unit based on1,3-insertion.

That is, this polymer 6 did not meet the above requirement (b) of thethird associated invention.

The water vapor transmission rate Y after molding into a film was 15.0(g/m²/24 hr).

In polymer 6, the melting point Tm was 146° C., and thus, Y should be inthe range of 5.8≦Y≦11.8. However, Y was not in that range.

That is, polymer 6 did not meet the above requirement (c) of the thirdassociated invention.

The results of the above production examples 1 to 6 are shown in Table5. TABLE 5 category of propylene polymer polymer 1 polymer 2 polymer 3polymer 4 polymer 5 polymer 6 (propylene (propylene (propylene(propylene (propylene (propylene polymer [A]) polymer [A]) polymer [A])polymer [A]) polymer [B]) polymer [B]) production example productionproduction production production production production example 1 example2 example 3 example 4 example 5 example 6 composition of propylene (mol%) 100 100 97 95.4 100 96.1 polymer ethylene (mol %) — — 3 — — 3.91-butene (mol %) — — — 4.6 — — content of position [2, 1] insertion 1.320.89 1.06 1.23 0 0 irregularity unit (%) [1, 3] insertion 0.08 0.0050.16 0.09 0 0 melting point Tm (° C.) 146 152 141 142 165 146 watervapor transmission rate 10.5 9.5 12 11.5 7.8 8.3 (g/m²/24 hr) mmfraction (%) 99.7 99.8 99.2 99.3 97.6 97 MFR (g/10 minutes) 10 2 14 6 712In the table, “—” in the “ethylene” and “1-butene” section indicatesthat a polymer has been produced without using “ethylene” or “1-butene”.

As shown by the data in Table 5, polymers 1 to 4 meet the aboverequirement (a) to (c) of the third associated invention, and areequivalent to the above propylene polymer [A]. In addition, polymers 1to 4 meets the above requirements (d) and (e) of the third associatedinvention.

On the other hand, polymers 5 and 6 meet the above requirement (a) ofthe third associated invention, but fall to meet the above requirements(b) and (c). That is, polymers 5 and 6 are equivalent to the abovepropylene polymer [B].

A description will be given with respect to Examples in which apolypropylene resin composition and polypropylene resin expandedparticles were produced by using a variety of propylene polymers(polymers 1 to 6) obtained by the above production examples 1 to 6, andfurther, a molded article was produced by using the polypropylene resinexpanded particles.

Example 31

Polymer 1 (propylene polymer [A]) obtained in Production Example 1 andpolymer 5 (polypropylene polymer [B]) obtained in Production Example 5were mixed at 90:10 (ratio by weight). Then, two antioxidants (0.05% byweight of trade name “Yoshinox BHT” available from YoshitomiPharmaceuticals Co., Ltd. and 0.10% by weight of trade name “Irganox1010” available from Ciba Geigy Co., Ltd.) were added to this mixture,and the resultant polymer was extruded in a strand shape of 1 mm in sizeby a single screw extruder machine of 65 mm in size. Then, the extrudedpolymer was cooled in a water tank; and was cut into 2 mm in length,whereby a fine-granule pellet of a polypropylene resin composition wasobtained.

When DSC measurement was performed for the thus obtained polypropyleneresin composition, one endothermic peak was exhibited, and the peaktemperature was 153° C.

Next, by using this polypropylene resin composition as a base resin,polypropylene resin expanded particles were fabricated as follows.

First, 1000 g of a pellet shaped polypropylene resin composition was putinto a 5 L autoclave together with 2500 g of water, 200 g of calciumtertiary phosphate, 0.2 g of sodium dodecylbenzenesulfonate. Further,120 g of isobutane as the above blowing agent was added, and thetemperature was raised up to 140° C. over 60 minutes. Thereafter, thereaction mixture was maintained at this temperature for 30 minutes.

Thereafter, while supplying nitrogen gas into the autoclave so as tomaintain the pressure at 2.3 MPa, a valve at the bottom part of theautoclave was opened. Then the contents were discharged into anatmosphere of air.

By the above operation, polypropylene resin expanded particles wereobtained.

In addition, after drying the polypropylene resin particles, the bulkdensity was measured, the result was 42 g/L. In addition, the averagefoam size of the polypropylene resin expanded particles were 250 micronin its average size, which were very uniform.

The average size of the foam of the above polypropylene resin expandedparticles indicates an average value of the size by selecting 50 foamsat random by a micro graph (or an image obtained by picturing thesectional plane on a screen) obtained by observing with a microscope asectional plane of the expanded particles cut so as to pass asubstantial center part of the expanded particles.

Next, by using the above polypropylene resin expanded particles, amolded article was fabricated as follows.

First, the above obtained polypropylene resin expanded particles weresequentially charged under compression into an aluminum mold from ahopper by using compressed air. Then, heating and molding were carriedout by introducing a steam of 0.30 MPa (gauge pressure) into the chamberof the mold, and a molded article was obtained.

This molded article had 0.060 g/cm³ of density, a dimension of 300 mmvertical, 300 mm horizontal, and 50 mm in thickness. The molded articlehad little voids on the surface, having superior surface appearance freeof irregularities. In addition, when the degree of fusion of a crosssection was measured by breaking the article at the center of it, theresult was 90%.

With respect to the above degree of fusion, after the molded article wasbroken, the number of particle breaks and the number of inter-particlebreaks on its sectional plane were visually counted, and the countedbreaks were expressed by a ratio of the number of particle breaks withrespect to a total number of both of them.

In addition, a test specimen of a dimension of 50 mm vertical, 50 mmhorizontal, and 25 mm in thickness was prepared from another moldedarticle molded under the same molding condition. Then, a compressiontest was carried out in conformance with JIS K6767. The stress during50% compression was 7.5 kg/cm². Further, using a test specimen of thesame size, when a permanent set after compression was measured by themethod described in JIS K6767, the result was 11%.

These results were shown in Table 6 below.

(Examples 32 to 37) and (Comparative Examples 31 and 32)

Next, a composition of the polypropylene resin composition used as abase resin of propylene resin expanded particles was changed, andpolypropylene resin expanded particles and a molded article werefabricated in the same manner as in Example 31.

As a base resin, there was used a polypropylene resin composition inwhich the polymers 1 to 6 obtained in the production examples 1 to 6were prepared at the compositions described in Table 6.

Then, the polypropylene resin expanded particles and molded article werefabricated by using the above polypropylene resin composition, andevaluation of these was performed in the same manner as in Example 31.

The results are shown in Tables 6 and 7. TABLE 6 Example Example 31Example 32 Example 33 Example 34 Example 35 Example 36 Example 37composition (ratio polymer 1/ polymer 1/ polymer 1/ polymer 2/ polymer3/ polymer 4/ polymer 2/ by weight) polymer5 = polymer 5 = polymer 5 =polymer 5 = polymer 5 = polymer 5 = polymer 6 = 90/10 50/50 10/90 95/530/70 50/50 90/10 melting point (° C.) 153 158 161 157 159 156 156 ofresin composition foaming temperature 140 145 150 145 150 145 146 (° C.)bulk density of 42 45 47 40 45 45 45 expanded particle (g/L) conditionof foam average size average size average size average size average sizeaverage size average size 280 μm; 220 μm; 250 μm; 300 μm; 250 μm; 220μm; 250 μm; highly uniform highly uniform highly uniform highly uniformhighly uniform highly uniform highly uniform density of expanded 60 6060 60 60 60 60 article (g/L) steam pressure for 0.3 0.3 0.35 0.3 0.350.35 0.35 molding (MPa) degree of fusion (%) 90 80 90 80 90 95 85appearance of ◯ ◯ ◯ ◯ ◯ ◯ ◯ molded article compression test 7.5 8.3 9.18.4 8.8 8.5 12 (kg/cm²) permanent set after 11 12 13 12 13 12 11compression (%)

TABLE 7 Comparative Comparative Example 31 Example 32 composition (ratioby weight) polymer1 = 100 polymer5 = 100 melting point (° C.) of resin146 165 composition foaming temperature (° C.) 135 150 bulk density ofexpanded particle 45 46 (g/L) condition of foam average size averagesize 210 μm; 170 μm; uniform widely varied density of expanded article(g/L) 60 60 steam pressure for molding 0.3 0.3 (MPa) degree of fusion(%) 90 40 appearance of the molded article X˜Δ X compression test(kg/cm²) 7.3 4.5 permanent set after compression 11 16 (%)

As shown by the data in Tables 6 and 7, in Examples 31 to 37 accordingto the present invention, it was found that foams of polypropylene resinexpanded particles is very uniform; a molded article using them is highin degree of fusion; and further, the surface appearance is excellent.In addition, with respect to mechanical properties, the compressionstrength was high, and the permanent set after compression strain wassmall.

In contrast, in the case where the above polymer 1 obtained byProduction Example 1 was used independently, the surface appearance of amolded article molded by using the obtained polypropylene resin expandedparticles was poor (Comparative Example 31). In addition, in the casewhere the above polymer 5 obtained by Production Example 5 was usedindependently, the obtained polypropylene resin expanded particles werelarge in deviation of the size of foams (Comparative Example 32).Further, the molded article molded by using the polypropylene resinexpanded particles were low in internal degree of fusion, and further,the surface appearance of the molded article was poor. Furthermore, themechanical properties were insufficient (Comparative Example 32).

Now, Examples of the fourth associated invention will be described here.

[Production 1 of Propylene Polymer]

First, propylene polymers [A] and [B] constituting a polypropylene resincomposition were synthesized by any of the methods shown in thefollowing Production Examples 1 to 6.

Production Example 1

(i) Synthesis of[dimethylsilylenebis{1,1′-(2-methyl-4phenyl-4-hydroazulenyl)}zirconiumdichloride]

All of the following reactions were performed in an inert gasatmosphere, and solvents were dried and purified before using in suchreactions.

(a) Synthesis of racemic/meso mixture

(b) Separation of racemic body

(ii) Synthesis of Catalyst

(a) Treatment of Catalyst Carrier

(b) Preparation of Catalyst Component

The above description is similar to that of Production Example 1 of thefirst associated invention.

(iii) Polymerization of Propylene (Production of Propylene Polymer A)

After a stirrer-equipped 200 L autoclave of was thoroughly substitutedwith propylene, 45 kg of dehydrated liquid propylene was introduced.Then, 500 mL (0.12 mol) of a hexane solution of triisobutyl aluminum andhydrogen (3 NL) were introduced, and the internal temperature of theautoclave was raised up to 70° C.

Thereafter, the above solid catalyst component (1.7 g) was put into theautoclave with pressure of argon, polymerization was started, andpolymerization reaction was carried out for 3 hours.

Thereafter, 100 mL of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 14.1 kgof a polymer was obtained.

This polymer is 100 mol % in structural obtained from propylene, i.e., apropylene homopolymer. This polymer meets the above requirement (a) ofthe fourth associated invention.

In addition, this polymer had the following properties: MFR (melt flowrate)=10 g/10 minutes; 99.7% of isotactic triad fraction; a meltingpoint of 146° C. measured by the DSC technique (the temperature wasraised at a rate of 10° C./minute from 30° C.) The polymer met the aboverequirements (d) and (e) of the fourth associated invention. Further, acontent of position irregularity unit based on 2,1-insertion was 1.32%;a content of position irregularity based on 1,3-insertion was 0.08%; andthe above requirement (b) of the fourth associated invention was met.

Hereinafter, the thus obtained polypropylene polymer is referred to as“polymer 1”.

(iv) Measurement of Water Vapor Transmission Rate

The above obtained polymer 1 was molded in a film of 25 micron inthickness, and the water vapor transmission rate Y was measured inaccordance with the method described in JIS K 7129 (this applies to thefollowing production examples) The result was 10.5 (g/m²/24 hr).

In polymer 1, as described above, the melting point Tm was 146° C. Fromthe above formula (1), Y should be in the range of 5.8≦Y≦11.8. Y was inthat range, meeting the above requirement (c) of the fourth associatedinvention.

Production Example 2 Production of Propylene Polymer [A] and PropyleneHomopolymerization

After a stirrer-equipped 200 L autoclave was thoroughly substituted withpropylene, 45 kg of dehydrated liquid propylene was introduced. Then,500 mL (0.12 mol) of a hexane solution of triisobutyl aluminum andhydrogen (3 NL) were introduced, and the internal temperature of theautoclave was raised up to 40° C.

Thereafter, the above solid catalyst component (3.0 g) was pressed-inwith argon, polymerization was started, and polymerization reaction wasperformed for 3 hours.

Thereafter, 100 mL of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 4.4 kgof a polymer was obtained.

This polymer is 100 mol % in structural obtained from propylene, i.e., apropylene homopolymer. This polymer meets the above requirement (a) ofthe fourth associated invention.

In addition, this polymer had the following properties: MFR=2; 99.8% ofisotactic triad fraction; a melting point of 152° C. measured by the DSCtechnique (the temperature was raised at a rate of 10° C./minute from30° C.). The polymer met the above requirements (d) and (e) of thefourth associated invention. Further, a content of position irregularityunit based on 2,1-insertion was 0.89%; a content of positionirregularity based on 1,3-insertion was 0.005%; and the aboverequirement (b) of the fourth associated invention was met.

Hereinafter, the thus obtained polypropylene polymer is referred to as“polymer 2”.

In addition, with respect to the polymer 2, when the water vaportransmission rate Y when the polymer is molded in film was investigatedas in the above polymer 1, the rate Y was 9.5 (g/m²/24 hr).

In polymer 2, as described above, the melting point Tm was 152° C. Thus,from the above formula (1), Y should be in the range of 4.6≦Y≦9.8. Y wasin that range, and thus, met the above requirement (c) of the fourthassociated invention.

Production Example 3 Production of Propylene Polymer [A] andPropylene/Ethylene Copolymerization

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was introduced.500 mL (0.12 mol) of a hexane solution of triisobutyl aluminum wasadded, and the internal temperature of the autoclave was raised up to70° C. Thereafter, the solid catalyst component (9.0 g) was added; a gasmixture of propylene and ethylene (propylene:ethylene −97.5:2.5 ratio byweight) was introduced so that the pressure becomes 0.7 MPa; andpolymerization reaction was performed for 3 hours under this condition.

Thereafter, 100 mL of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 9.3 kgof a polymer was obtained.

In this polymer, the content of the structural unit derived frompropylene was 97.0 mol %, and the content of the structural unit derivedfrom ethylene was 3. 0 mol %. This value met the above requirement (a)of the fourth associated invention.

In addition, this polymer had the following properties: MFR=14; 99.2% ofisotactic triad fraction; a melting point of 141° C. measured by the DSCtechnique (the temperature was raised at a rate of 10° C./minute from30° C.). The polymer met the above requirements (d) and (e) of thefourth associated invention. Further, a content of position irregularityunit based on 2,1-insertion was 1.06%; a content of positionirregularity unit based on 1,3-insertion was 0.16%; and the aboverequirement (b) of the fourth associated invention was met.

Hereinafter, the thus obtained polypropylene polymer is referred to as“polymer 3”.

In addition, with respect to the polymer 3, when the water vaportransmission rate Y when the polymer is molded in film was investigatedas in the above polymers 1 and 2, the rate Y was 12.0 (g/m²/24 hr).

In polymer 3, as described above, the melting point Tm was 141° C. Thus,from the above formula (1), Y should be in the range of 6.8≦Y≦13.5. Ywas in that range, and thus, met the above requirement (c) of the fourthassociated invention.

Production Example 4 Production of Propylene Polymer [A] andPropylene/1-Butene Copolymerization

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was introduced.500 mL (0.12 mol) of a hexane solution of triisobutyl aluminum wasadded, and the internal temperature of the autoclave was raised up to70° C. Thereafter, the solid catalyst component (9.0 g) was added; a gasmixture of propylene and 1-butene (propylene:1-butene 90:10 ratio byweight) was introduced so that the pressure becomes 0.6 MPa;polymerization was started; and polymerization reaction was performedfor 3 hours under this condition.

Thereafter, 100 mL of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 8.6 kgof a polymer was obtained.

In this polymer, the content of the structural unit derived frompropylene was 95.4 mol %, and the content of the structural unit derivedfrom ethylene was 4.6 mol %. This value met the above requirement (a) ofthe fourth associated invention.

In addition, this polymer had the following properties: MFR=6; a meltingpoint of 142° C. measured by the DSC technique (the temperature wasraised at a rate of 10° C./minute from 30° C.); 99.3% of isotactic triadfraction. Thereby the polymer met the above requirements (d) and (a) ofthe fourth associated invention. Further, a content of positionirregularity unit based on 2,1-insertion was 1.23%; a content ofposition irregularity unit based on 1,3-insertion was 0.09%; and theabove requirement (b) of the fourth associated invention was met.

Hereinafter, the thus obtained polypropylene polymer is referred to as“polymer 4”.

In addition, with respect to the polymer 4, when the water vaportransmission rate Y when the polymer is molded in film was investigatedas in the above polymers 1 to 3, the rate Y was 11.5 (g/m²/24 hr).

In polymer 4, as described above, the melting point Tm was 142° C. Thus,from the above formula (1), Y should be in the range of 6.6≦Y≦13.1. Ywas in that range, and thus, met the above requirement (c) of the fourthassociated invention.

Production Example 5 Production of Propylene Polymer [B] and PropyleneHomopolymerization

After the inside of the stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was introduced,and diethyl aluminum chloride (45 g) and 11.5 g of a titaniumtrichloride catalyst available from Marubeni Solvay Co., Ltd. wasintroduced under a propylene atmosphere. Further, while the hydrogenconcentration of a gas phase part was maintained at 7.0% by volume,propylene was introduced in the autoclave at the autoclave internaltemperature of 60° C. over 4 hours at a rate of 9 kg/hour.

After propylene introduction was stopped, reaction was further continuedfor 1 hour; 100 mL of butanol was added to the autoclave; the reactionwas stopped; and the residual gas was purged, whereby 26 kg of a polymerwas obtained. The thus obtained polymer is referred to as “polymer 5”.

This polymer is 100 mol % in structural unit derived from propylene,that is, is a propylene homopolymer. This polymer met the aboverequirement (a) of the fourth associated invention.

This polymer had the following properties: MFR=7; a melting point of165° C.; 97.6% of isotactic triad fraction; 0% of position irregularityunit based on 2,1-insertion; 0% of position irregularity unit based on1,3-insertion.

That is, this polymer did not meet the above requirement (b) of thefourth associated invention. Hereinafter, the polymer obtained here isdefined as “polymer 5”.

With respect to polymer 5, as in the above polymers 1 to 4, when thewater vapor transmission rate Y after molded in film was investigated,the result was 7.8 (g/m²/24hr). In polymer 5, as described above, themelting point Tm was 165° C., and thus, Y should be in the range of2.0≦Y≦5.6. However, Y was not in that range.

That is, polymer 5 did not meet the above requirement (c) of the fourthassociated invention.

Production Example 6 Production of Propylene Polymer [B] andPropylene/Ethylene Copolymerization

After the inside of the stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was introduced,and diethyl aluminum chloride (40 g) and 7.5 g of a titanium trichloridecatalyst available from Marubeni Solvay Co., Ltd. was introduced under apropylene atmosphere. Further, while the hydrogen concentration of a gasphase part was maintained at 7.0% by volume, a gas mixture of propyleneand ethylene (propylene:ethylene=97.5:2.5 at ratio by weight) wasintroduced at the autoclave internal temperature of 60° C. so that thepressure becomes 0.7 MPa.

After the gas mixture introduction was stopped, reaction was furthercontinued for 1 hour; 100 mL of butanol was added to the autoclave; thereaction was stopped; and the residual gas was purged, whereby 32 kg ofa polymer was obtained. The thus obtained polymer is referred to as“polymer 6”.

This polymer had 96.4 mol % of structural unit derived from propylene,and 3.9 mol % of structural unit derived from ethylene. This polymer metthe above requirement (a) of the fourth associated invention.

This polymer 6 had the following properties: MFR=12; a melting point of146° C.; 97.0% of isotactic triad fraction; 0% of position irregularityunit based on 2,1-insertion; 0% of position irregularity unit based on1,3-insertion.

That is, this polymer 6 did not meet the above requirement (b) of thefourth associated invention.

The water vapor transmission rate Y after molded in film wasinvestigated as in the above polymers 1 to 5, and the rate Y was 15.0(g/m²/24 hr). In polymer 6, the melting point Tm was 146° C., and thus,Y should be in the range of 5.8≦Y≦11.8. However, Y was not in thatrange.

That is, polymer 6 did not meet the above requirement (c) of the fourthassociated invention.

The results of the above production examples 1 to 6 are shown in Table8. TABLE 8 category of propylene polymer polymer 1 polymer 2 polymer 3polymer 4 polymer 5 polymer 6 propylene propylene propylene propylenepropylene propylene polymer [A] polymer [A] polymer [A] polymer [A]polymer [B] polymer [B] production example production productionproduction production production production example 1 example 2 example3 example 4 example 5 example 6 composition of propylene (mol %) 100.0100.0 97.0 95.4 100.0 96.4 polymer ethylene (mol %) — — 3.0 — — 3.61-butene (mol %) — — — 4.6 — — content of position [2, 1] insertion 1.320.89 1.06 1.23 0 0 irregularity unit (%) [1, 3] insertion 0.08 0.0050.16 0.09 0 0 melting point Tm (° C.) 146 152 141 142 165 146 watervapor transmission rate 10.5 9.5 12.0 11.5 7.8 15.0 (g/m²/24 hr) [mm]fraction (%) 99.7 99.8 99.2 99.3 97.6 97.0 MFR (g/10 minutes) 10 2 14 67 12In the table, “—” in the “ethylene” and “1-butene” section indicatesthat a polymer has been produced without using “ethylene” or “1-butene”.

As shown by the date in Table 8, polymers 1 to 4 meet the aboverequirement (a) to (c) of the fourth associated invention, and areequivalent to the above propylene polymer [A]. In addition, polymers 1to 4 further meet the above requirements (d) and (e) of the fourthassociated invention.

On the other hand, polymers 5 and 6 meet the above requirement (a) ofthe fourth associated invention, but fails to meet the aboverequirements (b) and (c). That is, polymers 5 and 6 are equivalent tothe above propylene polymer [B].

A description will be given with respect to Examples in which apolypropylene resin composition and polypropylene resin expandedparticles were produced by using various propylene polymers (polymers 1to 6) obtained by the above production examples 1 to 6, and further, amolded article was produced by using the polypropylene resin expandedparticles.

It should be noted that, in each of the examples below, a melting pointwas determined as follows:

<Melting Point>; By using a differential scanning calorimeter (DSC), thetemperature of 3 mg to 5 mg of sample consisting of a propylene polymerobtained in accordance with each of the above described productionexamples 1 to 6 or a resin of a coat layer written in Tables 9 and 10 tobe described later, was raised up to 220° C. from 30° C. at a rate of10° C./minute. Then, the temperature was lowered to 30° C. at a rate of10° C./minute, and further, a melting point was defined with a peaktemperature on an endothermic curve obtained by rising a temperature to220° C. at a rate of 10° C./minute again.

Example 41

By using a single screw extruder of 65 mm in internal diameter, polymer1 obtained in Production Example 1 and polymer 5 obtained in ProductionExample 5 were mixed at a weight ratio of 90:10; then two antioxidants(0.05% by weight of trade name “Yoshinox BHT” available from YoshitomiPharmaceuticals, Co., Ltd.) and 0.10% by weight trade name “Irganox1010” available From Ciba Geigy Co., Ltd.) were added for kneading.Meanwhile linear low density polyethylene (LLDPE) with density of 0.920g/cm³ and a melting point of 121° C. was kneaded by using a single screwextruder of 30 mm in internal diameter.

Next, from a die having a die orifice of 1.5 mm in size, the abovekneaded polymer 1 and 5 was applied as a material for a core layer, thelinear low density polyethylene was applied as a coat layer, and theselayers were extruded in a strand shape.

Further, this strand was cooled through a water tank; the cooled strandwas cut so that the weight of one piece is 1.0 mg, and a fine granulepellet was obtained as resin particles. When these resin particles wereobserved by a phase contrast microscope, the structure of them was suchthat a core layer was coated by a coat layer with thickness of 30 micron(refer to FIG. 1 of the first associated invention).

When DSC measurement of the thus obtained fine granule pellet wasperformed a portion obtained from a propylene polymer exhibits oneendothermic peak, and its peak temperature was 153° C.

Next, in order to obtain the above resin particles as expandedparticles, 1000 g of the above fine granule pellet was put into a 5 Lautoclave together with 2500 g of water, 36 g of calcium tertiaryphosphate, and 40 g of sodium dodecylbenzenesulfonate (2% watersolution). Further, 180 g of isobutane was added, the temperature wasraised up to 140° C. over 60 minutes, and the reaction mixture wasmaintained at this temperature for 30 minutes.

Then, while supplying nitrogen gas into the autoclave so as to maintainthe pressure at 2.3 MPa, a valve at the bottom part of the autoclave wasopened. Then contents were discharged into an atmosphere of air, andfoaming was carried out.

After drying the expanded particles obtained by the above operation, thebulk density was measured, the result was 45 g/L. In addition, theaverage size of the foam of the particles was 270 micron, which was veryuniform.

The average size of the foam of the above polypropylene resin expandedparticles indicates an average value of the size by selecting 50 foamsat random on a micro graph (or an image obtained by picturing thesectional plane on a screen) obtained by observing with a microscope asectional plane of the expanded particles cut so as to pass asubstantial center part of the expanded particles in random.

Next, the above obtained propylene resin expanded particles weresequentially charged under compression into an aluminum mold from ahopper by using compressed air. Thereafter, heating and molding werecarried out by introducing a steam of 0.16 MPa (gauge pressure) into thechamber of the mold, and a molded article was obtained.

The molded article had 60 kg/m³ of density, a dimension of 300 mmvertical, 300 mm horizontal, and 50 mm in thickness. The molded articlehad little voids on the surface having superior surface appearance freeof irregularities. In addition, the degree of fusion was 90%, andshrinking percentage of the mold dimensions was 1.6%

In addition, after a test specimen of a dimension of 50 mm vertical, 50mm horizontal, and 25 mm in thickness was prepared from another moldedarticle molded under the same molding condition, when a compression testwas carried out in conformance with JIS K7220, the stress during 50%compression was 0.73 MPa. Further, using a testing specimen of the samesize, when a permanent set after compression was measured in accordancewith the method described in JIS K6767, the result was 11%.

In addition, a test piece of a dimension of 200 mm vertical, 30 mmhorizontal, and 12.5 mm in thickness was prepared from another moldedarticle molded under the same molding condition. This test specimen wascut, the number of particle breaks and the number of inter-particlebreaks on its sectional plane were visually measured, and a rate (%) ofparticle breaks with respect to a total number of both of these breakswas defined as the degree of fusion.

Further, the degree of dimensional change after heating at 110° C. wasmeasured in conformance with JIS K6767, and was judged based on thefollowing criteria (heat resistance test)

-   O: The degree of dimensional change after heating was lower than 3%.-   Δ: The degree of dimensional change after heating was 3% to 6%.-   X: The degree of dimensional change after heating exceeds 6% The    result is shown in Table 9 below.

(Examples 42 to 50) and (Comparative Examples 41 and 42)

Polypropylene resin expanded particles and a molded article thereof werefabricated in the same manner as in Example 41 except that polymers 1 to6 described in Table 8 were prepared by compositions shown in Tables 9to 11, and a resin forming a coat layer is used as those described inTables 9 to 11. The results are as shown in Tables 9 to 11. TABLE 9Example Example 41 Example 42 Example 43 Example 44 Example 45 Example46 polypropylene core layer composition (ratio by polymer 1/ polymer 1/polymer 1/ polymer 1/ polymer 2/ polymer 3/ resin expanded weight)polymer 5 = polymer 5 = polymer 5 = polymer 5 = polymer 5 = polymer 5 =particle 90/10 50/50 10/90 10/90 95/5 30/70 melting point (° C.) 153 158161 161 96.4 159 of composite coat layer resin for coat layer LLDPELLDPE LLDPE HIPS LLDPE LLDPE density(g/cm³) 0.92 0.92 0.92 1.05 0.920.92 melting point (° C.) 121 121 121 none 121 121 thickness of coatlayer (μ) 30 30 60 30 30 30 weight of composite particle 1 1 1 1 1 1 perparticle (mg) foaming temperature (° C.) 140 145 150 150 145 150 averagebulk density of 45 45 45 45 45 45 expanded particle (g/L) average sizeof foam (μ) 270 250 240 240 280 270 condition of foam highly highlyhighly highly uniform highly uniform highly uniform uniform uniformuniform expanded steam pressure for molding (MPa) 0.16 0.17 0.19 0.170.17 0.19 molded article density of molded article (kg/m³) 60 60 60 6060 60 appearance of molded article ◯ ◯ ◯ ◯ ◯ ◯ mold-to-part shrinkage(%) 1.6 1.7 1.8 1.8 1.7 1.8 degree of fusion (%) 90 90 90 90 90 90compression test (MPa) 0.73 0.86 0.91 0.92 0.84 0.87 permanent set aftercompression (%) 11 11 12 12 11 11 heat resistance test ◯ ◯ ◯ ◯ ◯ ◯LLDPE: Linear Low Density Polyethylene [density: 0.920 g/cm³ and meltingpoint 121° C.]HIPS: HIPA grade name “HT60” available from A and M Polystyrene Co.,Ltd.

TABLE 10 Example Comparative Comparative Example 47 Example 48 Example41 Example 42 polypropylene core layer composition (ratio by weight)polymer 4/ polymer 2/ polymer 1 = 100 polymer 5 = 100 resin expandedpolymer 5 = polymer 6 = particle 50/50 90/10 melting point (° C.) ofcomposite 156 156 146 165 coat layer resin for coat layer LLDPE LLDPELLDPE LLDPE density (g/cm³) 0.92 0.92 0.92 0.92 melting point (° C.) 121121 121 121 thickness of coat layer (μ) 30 30 30 30 weight of compositeparticle per particle (mg) 1 1 1 1 foaming temperature (° C.) 145 145135 150 average bulk density of expanded particle (g/L) 45 45 45 45average size of foam (μ) 260 280 210 170 condition of foam highlyuniform highly uniform highly uniform highly uniform expanded steampressure for molding (MPa) 0.16 0.16 0.16 0.16 molded article density ofmolded article (kg/m³) 60 60 60 60 appearance of molded article ◯ ◯ ◯ ◯mold-to-part shrinkage (%) 1.8 1.8 2 2 degree of fusion (%) 90 90 90 40compression test (MPa) 0.83 0.84 0.68 0.41 permanent set aftercompression (%) 11 12 12 17 heat resistance test ◯ ◯ Δ ◯LLDPE: Linear Low Density Polyethylene [density: 0.920 g/cm³ and meltingpoint 121° C.]

TABLE 11 Example Example 49 Example 50 polypropylene core composition(ratio by weight) polymer1/polymer5 = 90/10 polymer1/polymer5 = 90/10resin expanded layer melting point (° C.) of composite 153 153 particlecoat resin for coat layer composition A LLDPE2 layer thickness of coatlayer (μ) 30 30 weight of composite particle per particle (mg) 1 1foaming temperature (° C.) 140 140 average bulk density of expandedparticle (g/L) 45 45 average size of foam (μ) 270 270 condition of foamhighly uniform highly uniform expanded steam pressure for molding (MPa)0.18 0.12 molded article density of molded article (kg/m³) 60 60appearance of molded article ◯ ◯ mold-to-part shrinkage (%) 1.6 1.6degree of fusion (%) 90 90 compression test (MPa) 0.72 0.69 permanentset after compression (%) 11 11 heat resistance test ◯ ◯composition A:(1) Linear low density polyethylene (density 0.920 and melting point120° C.) [100 parts by weight](2) “Polymer1” obtained in Production Example 1 [10 parts by weight](3) “Polymer5” obtained in Production Example 5 [10 parts by weight]LLDPE2: Linear Low Density Polyethylene (density 0.907 and melting point100° C.)

As shown by the data in Tables 9 to 11, in the case of using, as amaterial of the above core layer, only a resin obtained from the aboveProduction Examples 1 and 5 (Comparative Examples 41 to 42), a moldedarticle that was molded by the obtained polypropylene resin expandedparticles was inferior in heat resistance (Comparative Example 41) andin surface appearance (Comparative Example 42).

As to polypropylene resin expanded particles obtained from the aboveComparative Example 42, the size of the foams were not uniform. Inaddition, the molded article molded by using the polypropylene resinparticles was poor in surface appearance and insufficient in themechanical properties.

In contrast, in Examples 41 to 50 according to the present invention, itwas found that the size of the foams of polypropylene resin expandedparticles were very uniform; the degree of fusion of the molded articleusing the particles was high; and further, the surface appearance wasexcellent. Further, with respect to the mechanical properties, thecompression strength was high, the compression set was small, andfurther, heat resistance was excellent.

Now, Examples of the fifth associated invention will be described here.

[Production 1 of Propylene Polymer]

First, propylene polymers as the base resin were synthesized by any ofthe methods shown in the following Production Examples 1 to 4.

Production Example 1

(i) Synthesis of[dimethylsilylenebis{1,1′-(2-methyl-4phenyl-4-hydroazulenyl)}zirconiumdichloride]

All of the following reactions were performed in an inert gasatmosphere, and solvents were dried and purified before using in suchreactions.

(a) Synthesis of racemic/meso mixture

(b) Separation of racemic isomer

(ii) Synthesis of Catalyst

(a) Treatment of Catalyst Carrier

(b) Preparation of Catalyst Component

The above description is similar to that of Production Example 1 of thefirst associated invention.

(iii) Polymerization of Propylene

After substituting the inside of a stirrer-equipped 200 L autoclave withpropylene, 45 kg of dehydrated liquid propylene was added. Then, 500 mL(0.12 mol) of hexane solution of triisobutyl aluminum and hydrogen (3NL) were added, and the internal temperature of the autoclave was raisedup to 70° C.

Thereafter, the above solid catalyst component (1.7 g) was put into theautoclave with pressure of argon, polymerization was started, andpolymerization reaction was performed for 3 hours.

Thereafter, 100 mL of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 14.1 kgof a polymer was obtained.

This polymer is 100 mol % in structural unit derived from propylene,i.e., is a propylene homopolymer. This polymer meets the aboverequirement (a) of the fifth associated invention.

In addition, this polymer had the following properties: MFR (melt flowrate)=10 g/10 minutes; 99.7% of isotactic triad fraction; a meltingpoint of 146° C. measured by the DSC technique (the temperature wasraised at a rate of 10° C./minute from 30° C.). The polymer met theabove requirements (d) and (e) of the fifth associated invention.Further, a content of position irregularity unit based on 2,1-insertionwas 1.32%; a content of position irregularity based on 1,3-insertion was0.08%; and the above requirement (b) of the fifth associated inventionwas met.

Hereinafter, the thus obtained polymer is referred to as “polymer 1”.

(iv) Measurement of Water vapor transmission rate

The above obtained polymer 1 was molded into a film of 25 micron inthickness, and the water vapor transmission rate Y was measured inaccordance with the method described in JIS K 7129 (this applies to thefollowing production examples). The result was 10.5 (g/m/²/24 hr).

In this polymer 1, as described above, the melting point Tm was 146° C.From the above formula (1), Y should be in the range of 5.8≦Y≦11.8. Ywas in that range, and met the above requirement (c) of the fifthassociated invention.

Production Example 2 Propylene Homopolymerization

After the inside of a stirrer-equipped 200 L autoclave was fullysubstituted with propylene, 45 kg of dehydrated liquid propylene wasadded. Then, 500 mL (0.12 mol) of a dehydrated liquid of triisobutylaluminum and hydrogen (3 NL) were added, and the internal temperature ofthe autoclave was raised up to 40° C.

Thereafter, the above solid catalyst component (3.0 g) was put into theautoclave with a pressure of argon, polymerization was started, andpolymerization reaction was performed for 3 hours.

Thereafter, 100 mL of ethanol was put into the autoclave the reactionwas stopped, and the residual gas component was purged, whereby 4.4 kgof a polymer was obtained.

This polymer is 100 mol % in structural unit derived from propylene,i.e., a propylene homopolymer. This polymer meets the above requirement(a) of the fifth following properties: MFR=2; 99.8% of isotactic triadfraction; a melting point of 152° C. measured by the DSC technique (thetemperature was raised at a rate of 10° C./minute from 30° C.). Thepolymer met the above requirements (d) and (e) of the fifth associatedinvention. Further, a content of position irregularity unit based on2,1-insertion was 0.89%; a content of position irregularity based on1,3-insertion was 0.005%; and the above requirement (b) of the fifthassociated invention was met.

Hereinafter, the thus obtained polypropylene polymer is referred to as“polymer 2”.

In addition, with respect to the polymer 2, when the water vaportransmission rate Y when the polymer is molded into a film wasinvestigated as in the above polymer 1, the rate was 9.5 (g/m²/24 hr).

In polymer 2, as described above, the melting point Tm was 152° C. Thus,from the above formula (1), Y should be in the range of 4.6≦Y≦9.8. Y wasin that range, and thus, met the above requirement (c) of the fifthassociated invention.

Production Example 3 Propylene/Ethylene Copolymerization

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was added. 500 mL(0.12 mol) of a hexane solution of triisobutyl aluminum was added, andthe internal temperature of the autoclave was raised up to 70° C.Thereafter, the solid catalyst component (9.0 g) was added; a mixturegas of propylene and ethylene (propylene:ethylene=97.5:2.5 at a ratio byweight) was added so that the pressure is 0.7 MPa; polymerization wasstarted; and polymerization reaction was performed for 3 hours underthis condition.

Thereafter, 100 mL of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 9.3 kgof a polymer was obtained.

In this polymer, the content of the structural unit derived frompropylene was 97.0 mol %, and the content of the structural unit derivedfrom ethylene was 3.0 mol %. This value met the above requirement (a) ofthe fifth associated invention.

In addition, this polymer had the following properties; MFR=14 g/10minutes; 99.2% of isotactic triad fraction; a melting point of 141° C.measured by the DSC technique (the temperature was raised at a rate of10° C./minute from 30° C.). The polymer met the above requirements (d)and (e) of the fifth associated invention. Further, a content ofposition irregularity unit based on 2,1-insertion was 1.06%; a contentof position irregularity based on 1,3-insertion was 0.16%; and the aboverequirement (b) of the fifth associated invention was met.

Hereinafter, the thus obtained polymer is referred to as “polymer 3”.

In addition, with respect to the polymer 3, when the water vaportransmission rate Y when the polymer is molded into a film wasinvestigated as in the above polymers 1 and 2, the rate was 12.0(g/m²/24hr).

In polymer 3, as described above, the melting point Tm was 141° C. Thus,from the above formula (1), Y should be in the range of 6.8≦Y≦13.5. Ywas in that range, and thus, met the above requirement (c) of the fifthassociated invention.

Production Example 4 Propylene/1-Butene Copolymerization

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was added. 500 mL(0.12 mol) of a hexane solution of triisobutyl aluminum was added, andthe internal temperature of the autoclave was raised up to 70° C.Thereafter, the solid catalyst component (9.0 g) was added; a mixturegas of propylene and 1-butene(propylene:1-butene 90:10 at a ratio byweight) was added so that the pressure is 0.6 MPa; polymerization wasstarted; and polymerization reaction was performed for 3 hours underthis condition.

Thereafter, 100 mL of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 8.6 kgof a polymer was obtained.

In this polymer, the content of the structural unit derived frompropylene was 95.4 mol %, and the content of the structural unit derivedfrom butene was 4.6 mol %. This value met the above requirement (a) ofthe fifth associated invention.

In addition, this polymer had the following properties: MFR=6 g/10minutes; a melting point of 142° C. measured by the DSC technique (thetemperature was raised at a rate of 10° C./minute from 30° C.); 99.3% ofisotactic triad fraction. The polymer met the above requirements (d) and(e) of the fifth associated invention. Further, a content of positionirregularity unit based on 2,1-insertion was 1.23%; a content ofposition irregularity based on 1,3-insertion was 0.09%; and the aboverequirement of the fifth associated invention (b) was met.

Hereinafter, the thus obtained polypropylene is referred to as “polymer4”.

In addition, with respect to the polymer 4, when the water vaportransmission rate Y when the polymer is molded into a film wasinvestigated as in the above polymers 1 to 3, the rate was 11.5 (g/m²/24 hr).

In polymer 4, as described above, the melting point Tm was 142° C. Thus,from the above formula (1), Y should be in the range of 6.6≦Y≦13.1. Ywas in that range, and thus, met the above requirement (c) of the fifthassociated invention.

Production Example 5

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was added, anddiethyl aluminum chloride (45 g) and 11.5 g of a titanium trichloridecatalyst available from Marubeni Solvay Co., Ltd. was added under apropylene atmosphere. Further, while a hydrogen concentration of a gasphase part was maintained to be 7.0% by volume, propylene was added inthe autoclave at the autoclave internal temperature of 65° C. for 4hours at a rate of 9 kg/hour.

After propylene introduction was stopped, reaction was further continuedfor 1 hour; 100 mL of butanol was added to the reaction mixture to stopreaction; and the residual gas content was purged, whereby 30 kg of apolymer was obtained.

This polymer is 100 mol % in structural unit derived from propylene,that is, is a propylene homopolymer. This polymer met the aboverequirement (a) of the fifth associated invention.

This polymer had the following properties: MFR=10 g/10 minutes; amelting point of 160° C. measured by DSC technique (the temperature wasraised at a rate of 10° C./minute from 30° C.); 97.0% of isotactic triadfraction.

In addition, this polymer had 0% of position irregularity unit based on2,1-insertion and 0% of position irregularity unit based on1,3-insertion.

That is, this polymer did not meet the above requirement (b) of thefifth associated invention.

Hereinafter, the thus obtained polymer is referred to as “polymer 5”.

With respect to polymer 5, as in the above polymers 1 to 4, when thewater vapor transmission rate Y after molded into a film wasinvestigated, the result was 10.0 (g/m²/24 hr).

In polymer 5, as described above, the melting point Tm was 160° C., andthus, Y should be in the range of 3.0≦Y≦7.2. However, Y was not in thatrange.

That is, polymer 5 did not meet the above requirement (c) of the fifthassociated invention.

Production Example 6

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was added, anddiethyl aluminum chloride (40 g) and 7.5 g of a titanium trichloridecatalyst available from Marubeni Solvay Co., Ltd. was added under apropylene atmosphere. Further, while the hydrogen concentration of a gasphase part was maintained at 7.0% by volume, a mixture gas of propyleneand ethylene (propylene:ethylene=97.5:2.5 in ratio by weight) was addedin the autoclave at 60° C. so that the pressure is 0.7 MPa.

After mixture gas introduction was stopped, reaction was furthercontinued for 1 hour; 100 mL of butanol was added to the reactionmixture to stop reaction; and the residual gas component was purged,whereby 32 kg of a polymer was obtained.

This polymer had the following properties: MFR=12 g/10 minutes; amelting point of 146° C. measured by DSC technique (the temperature wasraised at a rate of 10° C./minute from 30° C.; and 96.0% of isotactictriad fraction.

In addition, this polymer had 0% of position irregularity unit based on2,1-insertion and 0% of position irregularity unit based on1,3-insertion. That is, this polymer 6 did not meet the aboverequirement (b) of the fifth associated invention.

Hereinafter, the thus obtained polymer is referred to as “polymer 6”.

With respect to the above polymer 6, when the water vapor transmissionrate Y after molded into film was investigated in the same manner as inthe above polymers 1 to 5, the result was 15.0 (g/m²/24 hr).

In polymer 6, the melting point Tm was 146° C., and thus, Y should be inthe range of 5.8≦Y≦11.8. However, Y was not in that range.

That is, polymer 6 did not meet the above requirement (c) of the fifthassociated invention.

The results of the above production examples 1 to 6 are shown in Table12. TABLE 12 category of propylene polymer polymer 1 polymer 2 polymer 3polymer 4 polymer 5 polymer 6 production example production productionproduction production production production example 1 example 2 example3 example 4 example 5 example 6 composition of polymer propylene (mol %)100.0 100.0 97.0 95.4 100.0 96.4 ethylene (mol %) — — 3.0 — — 3.61-butene (mol %) — — — 4.6 — — content of position [2, 1] insertion 1.320.89 1.06 1.23 0 0 irregularity unit (%) [1, 3] insertion 0.08 0.0050.16 0.09 0 0 melting point Tm (° C.) 146 152 141 142 160 146 watervapor transmission rate (g/m²/24 hr) 10.5 9.5 12.0 11.5 10.0 15.0 [mm]fraction (%) 99.7 99.8 99.2 99.3 97.0 96.0 MFR (g/10 minutes) 10 2 14 610 12In the table, “—” in the “ethylene” and “1-butene” section indicatesthat a polymer has been produced without using “ethylene” or “1-butene”.

As shown by the data in Table 12, polymers 1 to 4 meet the aboverequirement (a) to (c) of the fifth associated invention, and areequivalent to the propylene polymer as the above base resin. Inaddition, polymers 1 to 4 meet the above requirements (d) and (e) of thefifth associated invention.

On the other hand, polymers 5 and 6 meet the above requirement (a) ofthe fifth associated invention, but fails to meet the above requirements(b) and (c) of the fifth associated invention.

A description will be given with respect to Examples 51 to 56 in which ashock absorber was produced by using the polymers 1 to 6 obtained by theabove production examples 1 to 6.

Example 51

As shown in FIGS. 2 and 3, the shock absorber 1 of this Example ismolded for a core material of an automobile bumper so that the sectionalview is in a substantially U shaped on a plane vertical to itslongitudinal direction.

In addition, the shock absorber 1 has a skin layer 15 with high densityso as to cover its surface.

Now, a production method of the shock absorber 1 will be described here.

First, expanded particles which is a raw material for the shock absorberare produced as follows.

Two antioxidants (0.05% by weight of trade name “Yoshinox BHT” availablefrom Yoshitomi Pharmaceuticals Co., Ltd. and 0.10% by weight of tradename “Irganox 1010” available from Ciba Geigy Co., Ltd.) were added tothe propylene homopolymer (polymer 1) serving as a base resin obtainedin Production Example 1, and the mixture was extruded into the form ofstrands of 1 mm in diameter using a 65 mm single screw extruder. Then,the extruded polymer was cooled in water; and was cut into pelletshaving length of 2 mm, whereby a fine-granule pellet of a polypropyleneresin composition was obtained.

1000 g of this pellet was put into a 5 L autoclave together with 2500 gof water, 200 g of calcium tertiary phosphate, 0.2 g of sodiumdodecylbenzenesulfonate. Further, 85 g of isobutane was added, and thetemperature was raised up to 135° C. over 60 minutes. Thereafter, thereaction mixture was maintained at this temperature for 30 minutes.

Thereafter, while supplying nitrogen gas into the autoclave so as tomaintain the pressure at 2.3 MPa, a valve at the bottom part of theautoclave was opened. Then the contents were discharged into anatmosphere of air.

In addition, after drying the expanded particles obtained by the aboveoperation, the bulk density was measured, and the result was 48 g/L. Inaddition, the average size of the foams of the polypropylene resinexpanded particles were 310 micron were very uniform.

The average size of the foam of the above expanded particles indicatesan average value of the size by selecting 50 foams at random on a micrograph (or an image obtained by projecting the sectional plane on ascreen) obtained by observing with a microscope a sectional plane of theexpanded particles cut so as to pass a substantial center part of theexpanded particles in random.

Next, the shock absorber 1 shown in FIGS. 2 and 3 was fabricated bymolding the above obtained expanded particles.

Specifically, after the above described expanded particles were chargedinto a cavity of an aluminum mold, heating and molding were carried outby introducing a steam of 0.28 MPa (gauge pressure) into the chamber ofthe mold, whereby the shock absorber 1 shown in FIG. 2 was obtained.

At this time, at a portion at which the above expanded particles comeinto contact with the above mold, the expanded particles are partiallymelted, thereby fusing them each other. As shown in FIG. 3, the skinlayer 15 with a density which is higher than its inside was formed onthe surface of the shock absorber 1.

The shock absorber 1 was 60 g/L of density of its inside (a portionother than the skin layer), was less in void on the surface, was free ofirregularities, and was excellent in surface appearance.

In addition, when the shock absorber 1 was broken at the center part,and the degree of fusion of its section was measured, the result was80%.

By cutting the above shock absorber, and then, visually counting thenumber of particle breaks on its section and the number ofinter-particle breaks, the above degree of fusion was expressed at arate of particle breaks with respect to a total number of both of them.

A test specimen of a dimension of 50 mm vertical, 50 mm horizontal, and25 mm in thickness was prepared from an internal portion (a portionother than the skin layer)of another shock absorber 1 molded under thesame molding condition, and compression test was carried out inconformance with JIS K6767. Based on the thus obtained result, astress-strain curve was obtained (one example of which is shown in FIG.4). From this diagram, the stress at 50% compression was 0.73 MPa inthis Example.

In addition, energy-absorbing efficiency (%) was obtained by thefollowing formula.Energy-absorbing efficiency (%)={(area of OAB)/(area of OABC)}×100

That is, for the energy-absorbing efficiency (%), in the stress-straincurve as shown in FIG. 4, a value obtained by dividing an area at aportion enclosed by the line connecting points O, A, and B (area of aportion shaded in the figure) by an area of a figure whose points O, A,B, and C are defined as vertexes in shown in percentage.

Further, by using a test specimen of the same size, when a permanent setafter compression was measured by the method described in JIS K6767, theresult was 11%.

The result was shown in Table 13 described later. The molding steampressure in Table 13 means a steam pressure at which a molded article(shock absorber) having 80% of fusion is obtained.

(Examples 52 to 54) and (Comparative Examples 51 and 52)

The above Examples and Comparative Examples were carried out in the samemanner as in Example 51 except that polymers described in Table 13 (theabove polymers 2 to 6) were used as a base resin.

The result is shown in Table 13 below. TABLE 13 Example ComparativeComparative Example 51 Example 52 Example 53 Example 54 Example 51Example 52 expanded particle base resin polymer 1 polymer 2 polymer 3polymer 4 polymer 5 polymer 6 expanding temperature 135 141 130 130 150135 (° C.) bulk density (g/L) 48 48 48 48 48 48 average size of foam (μ)310 280 300 300 200 180 condition of foam highly highly highly highlywidely varied widely varied uniform uniform uniform uniform shockabsorber steam pressure for 0.28 0.30 0.26 0.26 0.40 0.35 molding (MPa)density (g/L) 60 60 60 60 60 60 compression stress 0.73 0.81 0.69 0.760.52 0.43 (MPa) energy-absorbing 73.1 74.9 71.5 72.9 67.3 61.6efficiency (%) permanent set after 11 12 9 10 16 15 compression (%)

As shown by the data in Table 13, in the case where the polymers 5 and 6which do not meet the above requirements (b) and (c) of the fifthassociated invention, the polymers being obtained by the aboveproduction examples 5 and 6, were used as a base resin (in ComparativeExamples 51 and 52), the obtained expanded particles had foams with widedistribution in the size. Thus, a high molding steam pressure wasrequired to obtain a shock absorber with sufficient degree of fusionfrom these expanded particles.

In addition, with respect to these shock absorbers, the energy-absorbingefficiency was low, the performance at the shock absorber was notsatisfactory, and further, the permanent set after compression waslarge.

In contrast, in the case where the propylene polymers (polymers 1 to 4)obtained in accordance with production examples 1 to 4 each was used asa base resin (in Examples 51 to 54), the size of foams of the obtainedexpanded particles were very uniform, and the shock absorbers usingthese particles exhibited sufficient fusion at a low molding steampressure.

Further, the shock absorbers of Examples 51 to 54 were high inenergy-absorbing efficiency and compression stress, and were small inpermanent set after compression.

Thus, the shock absorbers of Examples 51 to 54 can be used as anexcellent core material for an automobile's bumper.

In addition, as shown in FIGS. 2 and 3, the shock absorbers 1 ofExamples 51 to 54 each have a skin layer 15. These shock absorbers 1 canbe used as a automobile bumper or the like.

Example 55

This Example shows an example of producing a shock-absorbing articlewhere a skin material is provided on the surface of the shock absorber.

The shock-absorbing article of this Example is an automobile'sdashboard, as shown in FIGS. 5 and 6.

In addition, as shown in FIGS. 5 and 6, the shock-absorbing article 3has a skin material 37 so as to cover a surface on one side of the shockabsorber 35 molded in a plurality of uneven shapes. In thisshock-absorbing article 3, the shock absorber 35 is made of expandedpropylene particles, and the skin material 37 is made of a polyolefinelastomer sheet.

Now, a method of producing the shock-absorbing article of this Examplewill be described here.

First, expanded particles similar to that of Example 51 were prepared. Afabrication method of the expanded particles is identical to those ofProduction Example 1 and Example 51 described above.

Next, a skin material was mounted on one side of the mold, and expandedparticles were charged.

Next, of a middle mold mounted to two molds which constitute a moldingtool, in the shock-absorbing article shown in FIG. 6, a sheet forforming a skin material is disposed in a mold (a recessed tool) formingthe side of the skin material 37, and mold clamping was performed.Further, expanded particles were charged in the above molding tool.

Thereafter, the resultant expanded particles were heated and molded byintroducing a steam of 0.28 MPa in gauge pressure into the chamber ofthe mold, and the shock-absorbing articles 3 shown in FIGS. 5 and 6 wereobtained.

The obtained shock-absorbing article 3 was 60 g/L of density of theshock absorber 35, was small in surface clearance, was free ofirregularities, and was excellent in surface appearance.

As shown in FIGS. 5 and 6, the shock-absorbing article 3 has a skinmaterial 37 so as to cover a surface on one side of the shock absorber35 which is similar to that of Example 51.

Thus, in the above shock-absorbing article 3, there is providedadvantageous effect that the above shock absorber 35 absorbs shockenergy, as described above; and the skin material 37 provided on thesurface of the above shock absorber 35 improves the strength of theshock-absorbing article 3, and beautifies the surface of theshock-absorbing article 3.

Now, Examples of the sixth associated invention will be described here.

[Production 1 of Propylene Polymer]

First, propylene polymers [A] and [B] were synthesized by any of themethods shown in the following Production Examples 1 to 6.

Production Example 1

(i) Synthesis of[dimethylsilylenebis{1,1′-(2-methyl-4-phenyl-4-hydroazulenyl)}zirconiumdichloride]

All of the following reactions were performed in an inert gasatmosphere, and solvents were dried and purified before using in suchreactions.

(a) Synthesis of racemic/meso mixture

(b) Separation of racemic isomer

(ii) Synthesis of Catalyst

(a) Treatment of Catalyst Carrier

(b) Preparation of Catalyst Component

The above description is similar to that of Production Example 1 of thefirst associated invention.

(iii) Polymerization of Propylene

After a stirrer-equipped 200 L autoclave was thoroughly substituted withpropylene, 45 kg of dehydrated liquid propylene was added. Then, 500 mL(0.12 mol) of hexane solution of triisobutyl aluminum and hydrogen (3NL) were added, and the internal temperature of the autoclave was raisedup to 70° C.

Thereafter, the above solid catalyst component (1.7 g) was put into theautoclave with pressure of argon, polymerization was started, andpolymerization reaction was carried out for 3 hours.

Thereafter, 100 mL of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 14.1 kgof a polymer was obtained.

This polymer is 100 mol % in structural unit derived from propylene,i.e., is a propylene homopolymer. This polymer meets the aboverequirement (a) of the sixth associated invention.

In addition, this polymer had the following properties: MFR (melt flowrate)=10 g/10 minutes; 99.7% of isotactic triad fraction; the meltingpoint of 146° C. measured by the DSC technique (the temperature wasraised at a rate of 10° C./minute from 30° C.) The polymer met the aboverequirements (d) and (e) of the sixth associated invention. Further, acontent of position irregularity unit based on 2,1-insertion was 1.32%;the content of position irregularity unit based on 1,3-insertion was0.08%; and the above requirement (b) of the sixth associated inventionwas met.

Hereinafter, the obtained polypropylene polymer is referred to as“polymer 1”.

(iv) Measurement of Water vapor transmission rate

The above obtained polymer 1 was molded into a film of 25 micron inthickness, and the water vapor transmission rate Y was measured inaccordance with the method described in JIS K 7129 (this applies to thefollowing production examples) The result was 10.5 (g/m²/24 hr).

With respect to this polymer 1, as described above, the melting point Tmwas 146 C. From the above formula (1), Y should be in the range of5.8≦Y≦11.8. Y was in that range, and met the above requirement (c) ofthe sixth associated invention.

Production Example 2 Propylene Homopolymerization

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 45 kg of dehydrated liquid propylene wasadded. Then, 500 mL (0.12 mol) of a hexane solution of triisobutylaluminum and hydrogen (3 NL) were added, and the internal temperature ofthe autoclave was raised up to 40° C.

Thereafter, the above solid catalyst component (3.0 g) was put into theautoclave with pressure of argon, polymerization was started, andpolymerization reaction was carried out for 3 hours.

Thereafter, 100 mL of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 4.4 kgof a polymer was obtained.

This polymer is 100 mol % in structural unit derived from propylene,i.e., a propylene homopolymer. This polymer meets the above requirement(a) of the sixth associated invention.

In addition, this polymer had the following properties: MFR=2 g/10minutes; 99.8% of isotactic triad fraction; melting point of 152° C.measured by the DSC technique (the temperature was raised at a rate of10° C./minute from 30° C.). The polymer met the above requirements (d)and (e) of the sixth associated invention. Further, a content ofposition irregularity unit based on 2,1-insertion was 0.89%; a contentof position irregularity unit based on 1,3-insertion was 0.005%; and theabove requirement (b) of the sixth associated invention was met.

Hereinafter, the thus obtained polypropylene polymer is referred to as“polymer 2”.

In addition, with respect to the polymer 2, when the water vaportransmission rate Y after molding into a film was investigated as in theabove polymer 1, the result was 9.5 (g/m²/24 hr).

In polymer 2, as described above, the melting point Tm was 152° C. Thus,from the above formula (1), Y should be in the range of 4.6≦Y≦9.8. Y wasin that range, and thus, met the above requirement (c) of the sixthassociated invention.

Production Example 3 Propylene/Ethylene Copolymerization

After the inside of a stirrer-equipped 200 L autoclave of 200 L wasthoroughly substituted with propylene, 60 L of purified n-heptane wasadded. 500 mL (0.12 mol) of a hexane solution of triisobutyl aluminumwas added, and the internal temperature of the autoclave was raised upto 70° C. Thereafter, the solid catalyst component (9.0 g) was added; amixture gas of propylene and ethylene (propylene:ethylene=97.5:2.5 ratioby weight) was added so that the pressure is 0.7 MPa; polymerization wasstarted; and polymerization reaction was performed for 3 hours underthis condition.

Thereafter, 100 mL of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 9.3 kgof a polymer was obtained.

In this polymer, the content of the structural unit derived frompropylene was 97.0 mol %, and the content of the structural unit derivedfrom ethylene was 3.0 mol %. These values met the above requirement (a)of the sixth associated invention.

In addition, this polymer had the following properties: MFR=14 g/10minutes; 99.2% of isotactic triad fraction; a melting point of 141° C.measured by the DSC technique (a temperature was raised at a rate of 10°C./minute from 30° C.) The polymer met the above requirements (d) and(e) of the sixth associated invention. Further, a content of positionirregularity unit based on 2,1-insertion was 1.06%; a content ofposition irregularity unit based on 1,3-insertion was 0.16%; and theabove requirement (b) of the sixth associated invention was met.

Hereinafter, the thus obtained polypropylene polymer is referred to as“polymer 3”.

In addition, with respect to the polymer 3, when the water vaportransmission rate Y when the polymer is molded in film was investigatedas in the above polymers 1 and 2, the result was 12.0 (g/m²/24 hr).

In polymer 3, as described above, the melting point Tm was 141° C. Thus,from the above formula (1), Y should be in the range of 6.8≦Y≦13.5. Ywas in that range, and thus, met the above requirement (c) of the sixthassociated invention.

Production Example 4 Propylene/1-Butene Copolymerization

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was added. 500 mL(0.12 mol) of hexane solution of triisobutyl aluminum was added, and theinternal temperature of the autoclave was raised up to 70° C.Thereafter, the solid catalyst component (9.0 g) was added; a mixturegas of propylene and 1-butene (propylene:1-butene 90:10 ratio by weight)was added so that the pressure is 0.6 MPa; polymerization was started;and polymerization reaction was performed for 3 hours under thiscondition.

Thereafter, 100 mL of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 8.6 kgof a polymer was obtained.

In this polymer, the content of structural unit derived from propylenewas 95.4 mol %, and the content of the structural unit derived fromethylene was 4.6 mol %. This value met the above requirement (a) of thesixth associated invention.

In addition, this polymer had the following properties: MFR=6 g/10minutes; a melting point of 142° C. measured by the DSC technique (thetemperature was raised at a rate of 10° C./minute from 30° C.); 99.3% ofisotactic triad fraction. The polymer met the above requirements (d) and(e) of the sixth associated invention. Further, a content of positionirregularity unit based on 2,1-insertion was 1.23%; a content ofposition irregularity unit based on 1,3-insertion was 0.09%; and theabove requirement (b) of the sixth associated invention was met.

Hereinafter, the thus obtained polypropylene is referred to as “polymer4”.

In addition, with respect to the polymer 4, when the water vaportransmission rate Y after molding into a film was investigated as in theabove polymers 1 to 3, the result was 11.5 (g/m²/24 hr).

In polymer 3, as described above, the melting point Tm was 142° C. Thus,from the above formula (1), Y should be in the range of 6.6≦Y≦13.1. Ywas in that range, and thus, met the above requirement (c) of the sixthassociated invention.

Production Example 5 Production of Propylene Polymer [B] and PropyleneHomopolymerization

After the inside of the stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was added, anddiethyl aluminum chloride (45 g) and 11.5 g of a titanium trichloridecatalyst available from Marubeni Solvay Co., Ltd. was added under apropylene atmosphere. Further, while the hydrogen concentration of a gasphase part was maintained at 7.0% by volume, propylene was added in theautoclave at the autoclave internal temperature of 65° C. over 4 hoursat a velocity of 9 kg/hour.

After propylene introduction was stopped, reaction was further continuedfor 1 hour; 100 mL of butanol was added to the reaction mixture; thereaction was stopped; and the residual gas was purged, whereby 30 kg ofpolymer was obtained.

This polymer is 100 mol % in structural unit derived from propylene,that is, is a propylene homopolymer. This polymer met the aboverequirement (a) of the sixth associated invention.

This polymer had the following properties: MFR=7 g/10 minutes; a meltingpoint of 165° C. measured by the DSC technique; (the temperature wasraised at a rate of 10° C./minute from 30° C.); 97.6% of isotactic triadfraction.

In addition, this polymer had 0% of position irregularity unit based on2,1-insertion and 0% of position irregularity unit based on1,3-insertion.

That is, this polymer did not meet the above requirement (b) of thesixth associated invention,

Hereinafter, the thus obtained polymer is referred to as “polymer 5”.

With respect to polymer 5, as in the above polymers 1 to 4, when thewater vapor transmission rate Y after molding into a film wasinvestigated, the result was 7.8 (g/m²/24 hr). In polymer 5, asdescribed above, the melting point Tm was 165° C., and thus, Y should bein the range of 2.0≦Y≦5.6 from the above formula (1). However, Y was notin that range.

That is, polymer 5 did not meet the above requirement (c) of the sixthassociated invention.

Production Example 6 Production of Propylene Polymer [B] andPropylene/Ethylene Copolymerization

After the inside of the stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was added, anddiethyl aluminum chloride (40 g) and 7.5 g of a titanium trichloridecatalyst available from Marubeni Solvay Co., Ltd. was added under apropylene atmosphere. Further, while the hydrogen concentration of a gasphase part was maintained at 7.0% by volume, a mixture gas of propyleneand ethylene (propylene:ethylene=97.5:2.5 at ratio by weight) was addedat the autoclave internal temperature of 60° C. so that the pressure is0.7 MPa.

After mixture gas introduction was stopped, reaction was furthercontinued for 1 hour; 100 mL of butanol was added to the reactionmixture; reaction was stopped; and the residual gas was purged, whereby32 kg of polymer was obtained.

In this polymer the content of the structural unit obtained frompropylene was 96.4% mol, and the content of the structural unit derivedfrom ethylene was 3.6 mol %. This value meets the above requirement (a)of the sixth associated invention.

This polymer had the following properties: MFR=12 g/10 minutes; amelting point of 146° C. measured by the DSC technique (the temperaturewas raised at a rate of 10° C./minute from 30° C.); 96.0% of isotactictriad fraction.

In addition, this polymer had 0% of position irregularity unit based on2,1-insertion and 0% of position irregularity unit based on1,3-insertion. That is, this polymer did not meet the above requirement(b) of the sixth associated invention.

Hereinafter, the thus obtained polymer is referred to as “polymer 6”.

With respect to the above polymer 6, when the water vapor transmissionrate Y after molding into a film was investigated in the same manner asin the above polymers 1 to 5, the result was 15.0 (g/m²/24 hr).

In polymer 6, the melting point Tm was 146° C., and thus, Y should be inthe range of 5.8≦Y≦11.8 from the above formula (1). However, Y was notin that range.

That is, polymer 6 did not meet the above requirement (c) of the sixthassociated invention.

The results of the above production examples 1 to 6 are shown in Table14. TABLE 14 category of propylene polymer polymer 1 polymer 2 polymer 3polymer 4 polymer 5 polymer 6 (propylene (propylene (propylene(propylene (propylene (propylene polymer [A]) polymer [A]) polymer [A])polymer [A]) polymer [B]) polymer [B]) production example productionproduction production production production production example 1 example2 example 3 example 4 example 5 example 6 composition of propylene (mol%) 100.0 100.0 97.0 95.4 100.0 96.4 polymer ethylene (mol %) — — 3.0 — —3.6 1-butene (mol %) — — — 4.6 — — content of position [2,1] insertion1.32 0.89 1.06 1.23 0 0 irregularity unit (%) [1,3] insertion 0.08 0.0050.16 0.09 0 0 melting point Tm (° C.) 146 152 141 142 165 146 watervapor transmission rate 10.5 9.5 12.0 11.5 7.8 15.0 (g/m²/24 hr) [mm]fraction (%) 99.7 99.8 99.2 99.3 97.6 96.0 MFR (g/10 minutes) 10 2 14 67 12In the table, “—” in the “ethylene” and “1-butene” section indicatesthat a polymer has been produced without using “ethylene” or “1-butene”.

As shown by the data in Table 14, polymers 1 to 4 meet the aboverequirements (a) to (c) of the sixth associated invention, and areequivalent to the above propylene polymer [A]. In addition, polymers 1to 4 meet the above requirements (d) and (e) of the sixth associatedinvention.

On the other hand, polymers 5 and 6 meet the above requirement (a) ofthe sixth associated invention, but fail to meet the above requirements(b) and (c). That is, polymers 5 and 6 are equivalent to the abovepropylene polymer [B].

Now, a description will be given with respect to Examples 61 to 66 inwhich shock absorbers are produced by using the polymers 1 to 6 obtainedby the above described Production Example 1 to 6.

Example 61

As shown in FIGS. 2 and 3 shown in the fifth associated invention, theshock absorber 1 of this Example is molded for a core material of anautomobile's bumper so that the sectional view is in a substantially Ushaped on a plane vertical to its longitudinal direction. In addition,the shock absorber 1 has a skin layer 15 with high density so as tocover its surface.

Now, a production method of the shock absorber 1 will be described here.

First, expanded particles which are a raw material of a shock absorberare produced as follows.

The above polymer 1 (equivalent to propylene polymer [A]) obtained byProduction Example 1 is mixed with the above polymer 5 (equivalent topropylene polymer [B]) obtained by Production Example 5 in 90:10 (ratioby weight), and two antioxidants (0.05% by weight of trade name“Yoshinox BHT” available from Yoshitomi Pharmaceuticals Co., Ltd. and0.10% by weight of trade name “Irganox 1010” available from Ciba GeigyCo., Ltd.) were added to this mixture, the added mixture was extrudedinto the form of strands of 1 mm in diameter using a 65 mm single screwextruder. Then, after cooling in water, the strands were cut intopellets having length of 2 mm

When DSC measurement of the thus obtained pellet was performed, oneendothermic peak was exhibited, and the peak temperature was 153° C.

1000 g of a pellet was put into a 5 L autoclave of together with 2500 gof water, 200 g of calcium tertiary phosphate, 0.2 g of sodiumdodecylbenzenesulfonate. Further, 85 g of isobutane was added, and thetemperature was raised up to 140° C. over 60 minutes. Thereafter, thereaction mixture was maintained at this temperature for 30 minutes.

Thereafter, while supplying nitrogen gas into the autoclave so as tomaintain the pressure at 2.3 MPa, a valve at the bottom part of theautoclave was opened. Then, the contents were discharged into anatmosphere of air.

After drying the expanded particles obtained by the above operation, thebulk density was measured, the result was 42 g/L. In addition, theaverage size of the foam of the particles was 250 micron, which was veryuniform.

The average size of the foam of the above expanded particles indicatesan average value of the size by selecting 50 foam at random on a micrograph (or an image obtained by picturing the sectional plane on ascreen) obtained by observing with a microscope a sectional plane of theexpanded particles cut so as to pass a substantial center part of theexpanded particles selected at random.

Next, the shock absorber 1 was fabricated by molding the above obtainedexpanded particles.

Specifically, after the above described expanded particles were chargedinto a cavity of an aluminum mold, heating and molding were carried outby introducing a steam of 0.30 MPa (gauge pressure) into the chamber ofthe mold, whereby the shock absorber 1 shown in FIG. 2 was obtained.

At this time, at a portion at which the above expanded particles comeinto contact with the above mold, the expanded particles are partiallymelted, thereby fusing them each other. As shown in FIGS. 2 and 3, theskin layer 15 with a density which is higher than that of its inside wasformed on the surface of the shock absorber 1.

The shock absorber 1 had 0.06 g/cm³ of density of its inside (a portionother than the skin layer), and had little voids on the surface havingsuperior surface appearance free of irregularities.

In addition, when the shock absorber 1 was broken at the center part,and the degree of fusion of its section was measured, the measurementwas 90%.

By cutting the above shock absorber, and then, visually counting thenumber of particle breaks on its section and the number ofinter-particle breaks, the above degree of fusion was expressed at arate of the number of particle breaks with respect to a total number ofboth of them.

In addition, a test specimen of a dimension of 50 mm vertical, 50 mmhorizontal, and 25 mm in thickness was prepared from an internal portion(a portion other than the skin layer) of another shock absorber 1 moldedunder the same molding condition, and compression test was carried outin conformance with JIS K6767. Based on the thus obtained result, astress-strain curve was obtained (one example of which is shown in FIG.4) From this diagram, the stress at 50% compression was 0.75 MPa in thisExample.

In addition, energy-absorbing efficiency (%) was obtained by thefollowing formula.Energy-absorbing efficiency (%)={(area of OAB)/(area of OABC)}×100

That is, for the energy-absorbing efficiency (%), in the stress-straincurve as shown in FIG. 4, a value obtained by dividing an area at aportion enclosed by the line connecting points O, A, and B (area of aportion shaded in the figure) by an area of a figure whose points O, A,B, and C are defined as vertexes is shown in percentage.

Further, by using a test specimen of the same size, when a permanent setafter compression was measured by the method described in JIS K6767, themeasurement was 11%.

The result was shown in Table 15 described later. The molding steampressure in Table 15 means a steam pressure at which a molded article(shock absorber) having 80% of fusion is obtained.

(Examples 62 to 67) and (Comparative Examples 61 and 62)

Testing was carried out in the same manner as in Example 61 except thatbase resins described in Table 15 were used.

The results are shown in Table 15 and Table 16 below. TABLE 15 ExampleExample 61 Example 62 Example 63 Example 64 Example 65 Example 66Example 67 expanded composition of base polymer 1/ polymer 1/ polymer 1/polymer 2/ polymer 3/ polymer 4/ polymer 2/ particle resin polymer 5 =polymer 5 = polymer 5 = polymer 5 = polymer 5 = polymer 5 = polymer 6 =90/10 50/50 10/90 95/5 30/70 50/50 90/10 melting point of base 153 158161 157 159 156 156 resin expanding temperature 140 145 150 145 150 145146 (° C.) bulk density (g/L) 42 45 47 40 45 45 45 average size of foam250 220 250 300 250 220 250 (μ) condition of foam highly highly uniformhighly uniform highly uniform highly uniform highly uniform highlyuniform uniform shock steam pressure for 0.30 0.30 0.35 0.30 0.35 0.350.35 absorber molding (MPa) density (g/cm³) 0.06 0.06 0.06 0.06 0.060.06 0.06 compression stress 0.75 0.83 0.91 0.84 0.88 0.85 0.81 (MPa)energy-absorbing 74.2 75.1 76.4 75.7 76.1 75.8 74.9 efficiency (%)permanent set after 11 12 13 12 13 12 11 compression (%)

TABLE 16 Comparative Comparative Example Example 61 Example 62 expandedcomposition of base resin polymer1 (only) polymer5 (only) particlemelting point of base resin 146 165 expanding temperature (° C.) 135 150bulk density (g/L) 48 48 average size of foam (μ) 310 200 condition offoam uniform widely varied shock steam pressure for molding (MPa) 0.280.40 absorber density (g/L) 60 60 compression stress (MPa) 0.73 0.52energy-absorbing efficiency (%) 73.1 67.3 permanent set aftercompression (%) 11 16

As shown by the data in Table 15, in the case where polymers 1 to 4equivalent to the above propylene polymer [A] and polymers 5 and 6equivalent to the propylene polymer [B] were used as a base resin(Examples 61 to 67), the foam of the obtained expanded particles is veryuniform in size, and a shock absorber using them exhibited sufficientfusion at a low molding steam pressure.

Further, the shock absorbers of Examples 61 to 67 were high inenergy-absorbing efficiency and compression stress, and were small inpermanent set after compression.

Thus, the shock absorbers of Examples 61 to 67 can be used as anexcellent core material for an automobile's bumper.

In addition, as shown in FIGS. 2 and 3 shown in the fifth associatedinvention, the shock absorbers 1 of Examples 61 to 67 each have a skinlayer 15. These shock absorbers 1 can be used as an automobile's bumperor the like.

In contrast, as shown by the data in Table 16, in the case where polymer1 equivalent to the above propylene polymer [A] was used independentlyas a base resin (Comparative Example 61), the obtained expandedparticles are not sufficient in uniformity of foam in size, andenergy-absorbing efficiency of the shock-absorbing article was notsufficient.

In addition, in the case where polymer 5 equivalent to the abovepropylene polymer [B] was used as a base resin (Comparative Example 62),the obtained expanded particles are great in deviation of foam in size.A high molding steam pressure was required in order to obtain the shockabsorber exhibiting the satisfactory degree of fusion by using theseexpanded particles. In addition, the shock absorber of ComparativeExample 62 was low in energy-absorbing efficiency, was unsatisfactory inperformance of the shock absorber, and further, was great in permanentset after compression.

Example 68

This Example shows an example of producing a shock-absorbing articlewhere a skin material is provided on the surface of the shock absorber.

The shock-absorbing article of this Example is an automobile'sdashboard, as shown in FIGS. 5 and 6 shown in the sixth associatedinvention.

In addition, as shown in FIGS. 5 and 6, the shock-absorbing article 3has a skin material 37 so as to cover a surface on one side of the shockabsorber 35 molded in a plurality of uneven shapes. In this shockabsorber 3, the shock absorber 35 is made of expanded polypropylene, andthe skin material 37 is made of a polyolefin elastomer sheet.

Now, a production method of a shock-absorbing article of this Examplewill be described here.

First, expanded particles similar to those of Example 61 described abovewere prepared. The production method of the expanded particles issimilar to that of Example 61 described above. That is, as a base resin,the expanded particles in this Example contains polymer 1 which is theabove propylene polymer [A] and polymer 5 which is the above propylenepolymer [B].

Next, of a middle mold mounted to two dies which constitute a mold, inthe shock-absorbing article shown in FIG. 6, a sheet for forming a skinmaterial is disposed in a die (a recessed die) forming the side of theskin material 37, and mold clamping was performed. Further, expandedparticles were charged in the above mold.

Thereafter, heating and molding were carried out by introducing a steamof 0.30 MPa (gauge pressure) into the chamber of the mold, and the shockabsorbers 3 shown in FIGS. 5 and 6 were obtained.

The obtained shock absorber 3 had 0.06 g/cm³ of density of the shockabsorber 35 of its inside, and had little voids of the surface havingsuperior surface appearance free of irregularities.

As shown in FIGS. 5 and 6, the shock absorber 3 has a skin material 37so as to cover a surface on one side of the shock absorber 35 which issimilar to that of Example 61.

Thus, in the above shock-absorbing article 3, there is providedadvantageous effect that the above shock absorber 35 absorbs shockenergy, as described above; and the skin material 37 provided on thesurface of the above shock absorber 35 improves the strength of theshock-absorbing article 3, and cleans the surface of the shock-absorbingarticle 3.

Now, examples of the seventh associated invention will be describedhere.

[Production of Base Resin]

First, a propylene polymer serving as a base resin was synthesized bythe following methods shown in Production Examples 1 to 4,

Production Example 1

(i) Synthesis of[dimethylsilylenebis{1,1′-(2-methyl-4-phenyl-4-hydroazulenyl)}zirconiumdichloride]

All of the following reactions were performed in an inert gasatmosphere, and solvents were dried and purified before using in suchreactions.

(a) Synthesis of racemic/meso mixture

(b) Separation of racemic isomer

(ii) Synthesis of Catalyst

(a) Treatment of Catalyst Carrier

(b) Preparation of Catalyst Component

The above description is similar to that of Production Example 1 of thefirst associated invention.

(iii) Polymerization of Propylene (Production of Propylene Polymer A)

After a stirrer-equipped 200 L autoclave was thoroughly substituted withpropylene, 45 kg of dehydrated liquid propylene was added. Then, 500 mL(0.12 mol) of a hexane solution of triisobutyl aluminum and hydrogen (3NL) were added, and the internal temperature of the autoclave was raisedup to 70° C.

Thereafter, the above solid catalyst component (1.7 g) was put into theautoclave with pressure of argon, polymerization was started, andpolymerization reaction was carried out for 3 hours.

Thereafter, 100 mL of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 14.1 kgof a polymer was obtained.

This polymer is 100 mol % in structural unit derived from propylene,i.e., a propylene homopolymer. This polymer meets the above requirement(a) of the seventh associated invention concerning the above propylenepolymer.

In addition, this polymer had the following properties: MFR (melt flowrate)=10 g/10 minutes; 99.7% of isotactic triad fraction; a meltingpoint of 146° C. measured by the DSC technique (the temperature wasraised at a rate of 10° C./minute from 30° C.). The polymer met theabove requirements (e) and (f) of the seventh associated invention.Further, the content of position irregularity unit based on2,1-insertion was 1.32%; the content of position irregularity based on1,3-insertion was 0.08%; and the above requirement (b) of the seventhassociated invention was met.

Hereinafter, the thus obtained polypropylene polymer is referred to as“polymer 1”.

(iv) Measurement of Water Vapor Transmission Rate

The above obtained polymer 1 was molded in a film of 25 micron inthickness, and the water vapor transmission rate A was measured inaccordance with the method described in JIS K 7129 (this applies to thefollowing production examples) The result was 10.5 (g/m²/24 hr).

In polymer 1, as described above, the melting point Tm was 146° C. Fromthe above formula (1), A should be in the range of 5.8≦A≦11.8. A is inthat range, and meets the above requirement (c) of the seventhassociated invention.

Production Example 2 Propylene/Ethylene Copolimerization

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was added. Then,500 mL (0.12 mol) of a hexane solution of triisobutyl aluminum wasadded, and the internal temperature of the autoclave was raised up to70° C. Thereafter, the above solid catalyst component (9.0 g) was added;a gas mixture of propylene and ethylene (propylene:ethylene=97.5:2.5,weight ratio) was added so that the pressure becomes 0.7 MPa;polymerization was started; and polymerization reaction was performedfor 3 hours.

Thereafter, 100 mL of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 9.3 kgof a polymer was obtained.

In this polymer, the structural unit derived from propylene exists to be97.0 mol %, and the structural unit derived from ethylene exists to be3.0 mol %. This polymer meets the above requirement (a) of the seventhassociated invention.

In addition, this polymer had the following properties: MFR=14 g/10minutes; 99.2% of isotactic triad fraction; a melting point of 141° C.measured by the DSC technique (the temperature was raised at a rate of10° C./minute from 30° C.). The polymer meets the above requirements (e)and (f) of the seventh associated invention. Further, a content ofposition irregularity unit based on2,1-insertion was 1.06%; and acontent of position irregularity based on 1,3-insertion was 0.16%, whichmeets the above requirement (b) of the seventh associated invention.Hereinafter, the thus obtained polypropylene polymer is referred to as“polymer 2”.

In addition, with respect to the polymer 2, the water vapor transmissionrate A obtained after the polymer was molded in film in the same manneras in the above polymer 1 was 12.0 (g/m²/24 hr).

In this polymer 2, as described above, the melting point Tm is 141° C.Thus, from the above formula (1), A should be in the range of6.8≦A≦13.5. A is in that range, and thus, meets the above requirement(c) of the seventh associated invention.

Production Example 3 Propylene/1-Butene Copolymerization

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was added. 500 mL(0.12 mol) of a hexane solution of triisobutyl aluminum was added, andthe internal temperature of the autoclave was raised up to 70° C.Thereafter, the solid catalyst component (9.0 g) was added; a gasmixture of propylene and ethylene (propylene:1-butene=90:10) was addedso that the pressure is 0.6 MPa; polymerization was started; andpolymerization reaction was performed for 3 hours under this condition.

Thereafter, 100 mL of ethanol was put into the autoclave, the reactionwas stopped, and the residual gas component was purged, whereby 8.6 kgof a polymer was obtained.

In this polymer, the content of the structural unit derived frompropylene was 95.4 mol %, and the content of the structural unit derivedfrom 1-butene was 4. 6 mol %. This value meets the above requirement (a)of the seventh associated invention.

In addition, this polymer had the following properties: MFR=6 g/10minutes; a melting point of 142° C. measured by the DSC technique (thetemperature was raised at a rate of 10° C./minute from 30° C.); 99.3% ofan isotactic triad fraction. The polymer meets the above requirements(e) and (f) of the seventh associated invention for propylene polymer.Further, a content of position irregularity unit based on 2,1-insertionwas 1.23%; and a content of position irregularity based on 1,3-insertionwas 0.09%, which meets the above requirement (b) of the seventhassociated invention. Hereinafter, the thus obtained polypropylenepolymer is referred to as “polymer 3”.

In addition, with respect to the polymer 3, when the water vaportransmission rate A when the polymer was molded in film was investigatedas in the above polymers 1 and 2, the rate A was 11.5 (g/m²/24 hr).

In polymer 3, as described above, the melting point Tm is 142° C. Thus,from the above formula (1), A should be in the range of 6.6≦A≦13.1. A isin that range, and thus, meets the above requirement (c) of the seventhassociated invention.

Production Example 4 Production of Propylene Polymer and PropyleneHomopolymerization

After the inside of a stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was added. 45 gof diethyl aluminum chloride and 11.5 g of titanium trichloride wereadded under a propylene atmosphere. Further, while the hydrogenconcentration of a gas phase part is maintained at 7.0% by volume,propylene was added into an autoclave at the autoclave internaltemperature of 65° C. over 4 hours at a rate of 9 kg/hour.

After introduction of the mixed gas was stopped, reaction was furthercontinued for 1 hour, 100 mL of butanol was added to the autoclave tostop the reaction, and the residual gas component was purged, whereby 30kg of a polymer was obtained. Hereinafter, the thus obtained polymer wasreferred to as “polymer 4”.

This polymer 4 contains a structural unit derived from propylene by 100mol %, that is, is obtained as a propylene homopolymer. This polymermeets the above requirement (a) of the seventh associated invention forthe propylene polymer.

In addition, the polymer 4 had the following properties: 7 g/10 minutesat MFR; melting point of 160° C. measured by the DSC technique (thetemperature was raised at a rate of 10° C./minute to 30° C.); and 97.0%of an isotactic triad fraction.

The polymer 4 had 0% of position irregularity unit based on2,1-insertion and 0% of position irregularity unit based on1,3-insertion. That is, the polymer 4 does not meet the requirement (b)of the seventh associated invention concerning the above propylenepolymer.

In addition, with respect to the polymer 4, when the water vaportransmission rate A when the polymer was molded in film was investigatedas in the above polymers 1 to 3, the rate was 10.0 (g/m²/24 hr).

In polymer 4, as described above, the melting point Tm is 160° C. Thus,from the above formula (1), A should be in the range of 3.0≦A≦7.2. Y isnot in that range, and thus, does not meet the above requirement (c) ofthe seventh associated invention.

Production Example 5 Production of Propylene Polymer andPropylene/Ethylene Copolymerization

After the inside of the stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was added, anddiethyl aluminum chloride (40 g) and 7.5 g of a titanium trichloridecatalyst available from Marubeni Solvay Co., Ltd. was added under apropylene atmosphere. Further, while the hydrogen concentration of a gasphase part was maintained at 7.0% by volume, a gas mixture of propyleneand ethylene (propylene:ethylene=97.5:2.5 ratio by weight) was added inthe autoclave at internal temperature of 60° C. so that the pressure is0.7 MPa.

After introduction of the mixed gas was stopped, reaction was furthercontinued for 1 hour; 100 mL of butanol was added to the autoclave; thereaction was stopped; and the residual gas was purged, whereby 32 kg ofa polymer was obtained. Hereinafter, the thus obtained polymer isreferred to as “polymer 5”.

In this polymer 5, the content of the structural unit derived frompropylene was 96.4 mol %, and the content of the structural unit derivedfrom ethylene was 3.6 mol %. These values meet the above requirement (a)of the seventh associated invention for a propylene polymer.

This polymer had the following properties: MFR=12 g/10 minutes; amelting point of 146° C. measured by the DSC technique (the temperaturewas raised at a rate of 10° C./minute from 30° C.); and 96.0% ofisotactic triad fraction.

In addition, the polymer 5 had 0% of position irregularity unit based on2,1-insertion and 0% of position irregularity unit based on1,3-insertion.

That is, this polymer 5 did not meet the above requirement (b) of theseventh associated invention.

With respect to polymer 5, as in the above polymers 1 to 4, when thewater vapor transmission rate A after molded in film was investigated,the result was 15.0 (g/m²/24 hr). In polymer 5, as described above, themelting point Tm is 146° C., and thus, A should be in the range of5.8≦A≦11.8. However, A is not in that range.

That is, polymer 5 does not meet the above requirement (c) of theseventh associated invention.

Production Example 6 Production of Propylene Polymer andPropylene/1-Butene Copolymerization

After the inside of the stirrer-equipped 200 L autoclave was thoroughlysubstituted with propylene, 60 L of purified n-heptane was added, and 45g of diethyl aluminum chloride and 15.0 g of a titanium trichloridecatalyst available from Marubeni Solvay Co., Ltd. was added under apropylene atmosphere. Further, while the hydrogen concentration of a gasphase part was maintained at 7.0% by volume, a gas mixture of propyleneand 1-butene (propylene:1-butene=90:10 at ratio by weight) was added atthe autoclave internal temperature of 60° C. so that the pressure is 0.6MPa.

After the gas mixture introduction was stopped, reaction was furthercontinued for 1 hour; 100 mL of butanol was added to the autoclave; thereaction was stopped; and the residual gas was purged, whereby 24 kg ofa polymer was obtained. The thus obtained polymer is referred to as“polymer 6”.

This polymer 6 had 96.9 mol % of structural unit derived from propyleneand 3.1 mol % of structural unit derived from 1-butene. This polymermeets the above requirement (a) of the seventh associated invention forpropylene polymer.

In addition, the polymer 6 had the following properties: 8 g/10 minutesat an MFR; a melting point of 150° C. measured by the DSC technique (thetemperature was raised at a rate of 10° C./minute from 30° C.) ; and95.4% of isotactic triad fraction.

The polymer 6 had 0% of position irregularity unit based on2,1-insertion and 0% of position irregularity unit based on1,3-insertion. That is, the polymer 6 does not meet the requirement (b)of the seventh associated invention concerning the propylene polymer.

In addition, as in the polymers 1 to 5, the water vapor transmissionrate A when the polymer 6 was molded in film was investigated, and themeasurement was 16.2 (g/m²/24 hr).

In the polymer 6, the melting point Tm is 150° C., and thus, from theabove formula (1), the degree of vapor penetrability A should be in therange of 5.0≦A≦10.5. However, A is not in that range.

That is, the polymer 6 did not meet the above requirement (c) of theseventh associated invention.

[Production of Expanded Particles]

Now, a description will be given with respect to Examples in whichexpanded particles are produced by using the above polymers 1 to 6obtained by Production Examples 1 to 6.

Example 71

Two antioxidants (0.05% by weight of trade name “Yoshinox BHT” availablefrom Yoshitomi Co., Ltd. and 0.10% by weight of trade name “Irganox1010” available from Ciba Geigy) were added to polymer 1 obtained inProduction Example 1; the added polymer was extruded in a strand mannerof 1 mm in size by means of a 65 mm single screw extruder. Then, theextruded polymer was cooled in a water tank, and was cut in length of 2mm, whereby a fine granule pellet was obtained.

1000 g of this pellet was put into a 5 L autoclave together with 2500 gof water, 200 g of calcium tertiary phosphate and 0.2 g of sodiumdodecylbenzenesulfonate. Further, 130 g of isobutane was added, thetemperature was raised up to 137° C. over 60 minutes, and the reactionmixture was maintained at this temperature for 30 minutes.

Thereafter, while supplying nitrogen gas into the autoclave so tomaintain the pressure at 2.3 MPa, a valve at the bottom part of theautoclave was opened. Then, the contents were discharged into anatmosphere of air.

After drying the expanded particles obtained by the above operation,when the bulk density was measured, the measurement was 21 g/L. Inaddition, foam of the expanded particles was 310 micron on average insize, which was very uniform. Hereinafter, the expanded particle isreferred to as “expanded particle A”.

With respect to the average size of the foam of the above expandedparticles, 50 foams were selected at random on a micro graph obtained byobserving with a microscope a sectional view of expanded particles cutso as to pass the substantial center part of the expanded particlesselected at random (or picture of this sectional plane on a screen), andan average value of these size is indicated.

Example 72

By using polymer 1 obtained by Production Example 1, expanded particleswere fabricated in the same manner as in the above Example 71 exceptthat a foaming temperature was set at 135° C. and an added amount ofisobutane was set at 118 g.

The bulk density of the expanded particles was 48 g/L. In addition foamof the expanded particles was 280 micron on average in size, which wasvery uniform. Hereinafter, this expanded particle was referred to as“expanded particle B”.

Example 73

By using polymer 2 obtained by Production Example 2, expanded particleswere fabricated in the same manner as in the above Example 71 exceptthat a foaming temperature was set at 130° C. and an added amount ofisobutane was set at 118 g.

The bulk density of the expanded particles was 48 g/L. In addition foamof the expanded particles was 300 micron on average in size, which wasvery uniform. Hereinafter, this expanded particle was referred to as“expanded particle C”.

Example 74

By using polymer 3 obtained by Production Example 3, expanded particleswere fabricated in the same manner as in the above Example 71 exceptthat a foaming temperature was set at 132° C. and an added amount ofisobutane was set at 120 g.

The bulk density of the expanded particles was 22 g/L. In addition, foamof the expanded particles was 300 micron on average in size, which wasvery uniform. Hereinafter, this expanded particle was referred to as“expanded particle D”.

Comparative Example 71

By using polymer 4 obtained by Production Example 4, expanded particleswere fabricated in the same manner as in the above Example 71 exceptthat a foaming temperature was set at 150° C.

The bulk density of the expanded particles was 22 g/L. In addition foamof the expanded particles was 200 micron on average in size, which waslarge in deviation. Hereinafter, this expanded particle was referred toas “expanded particle

Comparative Example 72

By using polymer 5 obtained by Production Example 5, expanded particleswere fabricated in the same manner as in the above Example 71 exceptthat a foaming temperature was set at 135° C.

The bulk density of the expanded particles was 21 g/L. In addition foamof the expanded particles was 180 micron on average in size, which waslarge in deviation. Hereinafter, this expanded particle was referred toas “expanded particle F”.

Comparative Example 73

Expanded particles were fabricated in the same manner as in the aboveComparative Example 72 except that an added amount of isobutane was setat 118 g.

The bulk density of the expanded particles was 48 g/L. In addition, foamof the expanded particles was 200 micron on average in size, which waslarge in deviation. Hereinafter, this expanded particle was referred toas “expanded particle G”.

Comparative Example 74

By using polymer 6 obtained in Production Example 6, expanded particleswere fabricated in the same manner as in the above Example 71 exceptthat a foaming temperature was set at 140° C.

The bulk density of the expanded particles was 22 g/L. Hereinafter, thisexpanded particle was referred to as “expanded particle H”.

The above results are shown in Table 17 and Table 18. TABLE 17 ExampleExample 71 Example 72 Example 73 Example 74 category of expandedparticle expanded expanded expanded expanded particle A particle Bparticle C particle D base resin base resin (production polymer 1polymer 1 polymer 2 polymer 3 example) (production (production(production (production example 1) example 1) example 2) example 3) MFR(g/10 minutes) 10 10 14 6 comonomer — — ethylene 1-butene contents ofcomonomer (mol %) — — 3.0 4.6 melting point (° C.) 146 146 141 142 watervapor transmission 10.5 10.5 12.0 11.5 rate (g/m²/24 hr) [mm] fraction(%) 99.7 99.7 99.2 99.3 [2,1] insertion (%) 1.32 1.32 1.06 1.23 [1,3]insertion (%) 0.08 0.08 0.16 0.09 expanded foaming temperature (° C.)137 135 130 132 particle bulk density (g/L) 21 48 48 22 average size offoam (μ) 310 280 300 300 condition of foam highly uniform highly uniformhighly uniform highly uniformIn the table, “—” of “comonomer” and “content of comonomer” sectionmeans polymerisation is conducted without adjunction of comonomer.

TABLE 18 Comparative Comparative Comparative Comparative Example 71Example 72 Example 73 Example 74 category of expanded particle expandedexpanded expanded expanded particle E particle F particle G particle Hbase resin base resin (production polymer 4 polymer 5 polymer 5 polymer6 example) (production (production (production (production example 4)example 5) example 5) example 6) MFR (g/10 minutes) 7 12 12 8 comonomer— ethylene ethylene 1-butene contents of comonomer (mol %) — 3.6 3.6 3.1melting point (° C.) 160 146 146 150 water vapor transmission rate 10.015.0 15.0 16.2 (g/m²/24 hr) [mm] fraction (%) 97.0 96.0 96.0 95.4 [2,1]insertion (%) 0 0 0 0 [1,3] insertion (%) 0 0 0 0 expanded foamingtemperature (° C.) 150 135 135 140 particle bulk density (g/L) 22 21 4822 average size of foam (μ) 200 180 200 180 condition of foam widelyvaried widely varied widely varied widely variedIn the table, “—” of “comonomer” and “content of comonomer” sectionmeans polymerisation is conducted without adjunction of comonomer.[Production of Polypropylene Resin Expanded Molded Article]

Now, a polypropylene resin expanded molded article was fabricated byusing the above expanded particles A to H obtained by the abovedescribed Examples 71 to 74 and Comparative Examples 71 to 74.

Example 75

After the expanded particle A obtained by Example 71 was sequentiallycharged under compression into an aluminum mold from a hopper by usingcompressed air with the compression ratio being defined as 24%, heatingand molding were carried out by introducing a steam of 0.28 MPa (gaugepressure) into the chamber of the mold. Then, a polypropylene resinexpanded molded article of 0.028 g/cm of density was fabricated.

In addition, from this polypropylene resin expanded molded article, atest specimen of a dimension of 290 mm vertical, 290 mm horizontal, and10 mm in thickness was prepared, and the degree of moisture permeabilitywas measured in conformance with ASTM E96.

In addition, from another molded element molded in the same moldingcondition, a test specimen of a dimension of 50 mm vertical, 50 mmhorizontal, and 25 mm in thickness was prepared, a compression test wascarried out in conformance with JIS K7220, and the stress during 50%compression was measured.

Further, from another molded element molded in the same moldingcondition, a test specimen of a dimension of 200 mm vertical, 30 mmhorizontal, and 12.5 mm in thickness was prepared, a heat resistancetest was performed in conformance with JIS K6767. Furthermore, thedegree of dimensional change after heating at 110° C. was measured, andthe heat resistance was judged in accordance with the followingcriteria.

-   O: The degree of dimensional change after heating is lower than 3%.-   Δ: The degree of dimensional change after heating is 3% to 6%.-   X: The degree of dimensional change after heating exceeds 6%.

The above result is shown in Table 19.

(Examples 76 to 86) and (Comparative Examples 73 to 86)

Types of, and molding conditions for, expanded particles are changed asshown in Tables 19 to 22 described later, and then, a polypropyleneresin expanded molded article was fabricated in the same manner as inExample 75 described above.

In addition, a test specimen was fabricated from these propylene resinexpanded molded articles in the same manner as in Example 75 describedabove, the degree of moisture permeability was measured, and further, acompression test and a heat resistance test were performed.

The results are shown in Tables 19 to 22.

The molding steam pressure in Tables 19 to 22 described above means asteam pressure at which a molded article with degree of fusion of 80% isprovided.

With respect the degree of fusion, a test specimen fabricated from amolded article was divided into two sections, the number of particlebreaks and the number of inter-particle breaks on its sectional planewere visually measured, and a rate (%) of particle breaks with respectto a total number of both of them was represented. TABLE 19 ExampleExample 75 Example 76 Example 77 Example 78 Example 79 Example 80molding category of expanded expanded expanded expanded expandedexpanded expanded condition particle particle A particle A particle Aparticle B particle B particle B compression ratio (%) 24 48 75 13 21 35evaluation result steam pressure for 0.28 0.28 0.28 0.28 0.28 0.28molding (MPa) density of molded 0.028 0.035 0.040 0.056 0.060 0.070article (g/cm³) moisture permeability 0.054 0.041 0.035 0.033 0.0320.030 (g/m²/hr) compression test 0.28 0.40 0.43 0.60 0.73 0.95 (MPa)heat resistance test ◯ ◯ ◯ ◯ ◯ ◯

TABLE 20 Example Example 81 Example 82 Example 83 Example 84 Example 85Example 86 molding category of expanded expanded expanded expandedexpanded expanded expanded condition particle particle C particle Cparticle C particle D particle D particle D compression ratio (%) 13 2135 20 48 70 evaluation result steam pressure for 0.26 0.26 0.26 0.260.26 0.26 molding (MPa) density of molded 0.056 0.060 0.070 0.028 0.0350.040 article (g/cm³) moisture permeability 0.033 0.031 0.029 0.0530.041 0.035 (g/m²/hr) compression test 0.57 0.69 0.90 0.29 0.42 0.45(MPa) heat resistance test ◯ ◯ ◯ ◯ ◯ ◯

TABLE 21 Comparative Comparative Comparative Comparative ComparativeComparative Example 75 Example 76 Example 77 Example 78 Example 79Example 80 molding category of expanded expanded expanded expandedexpanded expanded expanded condition particle particle E particle Eparticle E particle F particle F particle F compression ratio (%) 20 4870 24 48 75 evaluation result steam pressure for 0.40 0.40 0.40 0.350.35 0.35 molding (MPa) density of molded 0.028 0.035 0.040 0.028 0.0350.040 article (g/cm³) moisture permeability 0.059 0.049 0.042 0.0590.051 0.045 (g/m²/hr) compression test 0.24 0.33 0.36 0.23 0.31 0.34(MPa) heat resistance test Δ Δ Δ Δ Δ Δ

TABLE 22 Comparative Comparative Comparative Comparative ComparativeComparative Example 81 Example 82 Example 83 Example 84 Example 85Example 86 molding category of expanded expanded expanded expandedexpanded expanded expanded condition particle particle G particle Gparticle G particle H particle H particle H compression ratio (%) 13 2135 20 48 70 evaluation result steam pressure for 0.35 0.35 0.35 0.300.30 0.30 molding (MPa) density of molded 0.056 0.060 0.070 0.028 0.0350.040 article (g/cm³) moisture permeability 0.051 0.051 0.050 0.0590.048 0.043 (g/m²/hr) compression test 0.48 0.59 0.76 0.27 0.37 0.40(MPa) heat resistance test Δ Δ Δ ◯ ◯ ◯

As shown by the data in Tables 19 to 22, in the polypropylene resinexpanded molded article obtained by Examples 75 to 86, a relationshipbetween degree of moisture permeability Y (g/m²/hr) and density X(g/cm³) meets a relationship of the above formula (2), the degree ofmoisture permeability was low, and the moisture proofing properties wereexcellent. In addition, heat resistance and strength were excellent.Thus, this element was excellent as an architectural member or vehiclestructural member and the like.

Further, in comparing the polypropylene resin expanded molded article ofExamples 75 to 80 with those of Comparative Examples 75 to 77, theseelements each contain a polypropylene homopolymer as a base resin.However, in the polypropylene resin expanded molded article ofComparative Examples 75 to 77, a relationship between the degree ofmoisture permeability Y (g/m²/hr) and density X (g/cm³) does not meet arelationship of the above formula (2). When Examples 75 to 80 werecompared with Comparative Examples 75 to 77 in the substantiallyidentical molding condition, the polypropylene resins of Examples 75 to80 were excellent in heat resistance and strength. In addition, thedegree of moisture permeability was lower, and the moisture proofingproperties were more excellent as compared with Comparative Examples 75to 77.

In comparing the polypropylene resin expanded molded articles ofExamples 81 to 83 and those of Comparative Examples 78 to 83, theseelements each contain a copolymer between propylene and ethylene as abase resin. However, in the polypropylene resin expanded molded articlesof Comparative Examples 78 to 83, a relationship between the degree ofmoisture permeability Y (g/m²/hr) and density X (g/cm³) does not meet arelationship of the above Formula (2). In addition, when examples 81 to83 are compared with Comparative Examples 78 to 83, respectively, in thesubstantially same molding condition, the polypropylene resin expandedmolded articles of Examples 81 to 83 are excellent in heat resistanceand strength, were lower in degree of moisture permeability, and aremore excellent in moisture proofing properties, as compared withComparative Examples 78 to 83.

In comparing the polypropylene resin expanded molded articles ofExamples 84 to 86 and those of Comparative Examples 84 to 86, theseelements each contain a copolymer of propylene and 1-butene. However, inthe polypropylene resin expanded molded articles of Comparative Examples84 to 86, the relationship between degree of moisture permeability Y(g/m²/hr) and density X (g/m³) do not meet a relationship of the aboveformula (2). In addition, when Examples 84 to 86 are compared withComparative Examples 84 to 86, respectively, in the substantially samemolding condition, the polypropylene resin expanded molded articles ofExamples 84 to 86 is excellent in heat resistance and strength, is lowin degree of moisture permeability, and is excellent in moistureproofing properties, as compared with those of Comparative Examples 84to 86.

1-77. (canceled)
 78. A polypropylene resin composition, comprising: 5%by weight to 95% by weight of a propylene polymer [A]; and 95% by weightto 5% by weight of a propylene polymer [B] wherein the total amount ofpropylene polymers [A] and [B] is 100% by weight, the propylene polymer[A] has (a) 100 to 85 mole % of a structural unit derived from propyleneand 0 to 15 mole % of a structural unit derived from ethylene and/oralpha-olefin having 4 to 20 carbons wherein the total amount of thestructural unit derived from propylene and the structural unit derivedfrom ethylene and/or alpha-olefin having 4 to 20 carbons is 100 mole %;(b) 0.5% to 2.0% of a position irregularity unit based on 2,1-insertionof a propylene monomer unit in all propylene insertions, and 0.005% to0.4% of a position irregularity unit based on 1,3-insertion of propylenemonomer unit in all propylene insertions, as measured by 13 C-NMR; andthe propylene polymer [B] has 100 to 85 mole % of a structural unitderived from propylene, and 0 to 15 mole % of a structural unit derivedfrom ethylene and/or alpha-olefin having 4 to 20 carbons wherein thetotal amount of the structural unit derived from propylene and thestructural unit derived from ethylene and/or alpha-olefin having 4 to 20carbons is 100 mole %.
 79. The polypropylene resin composition asclaimed in claim 78, wherein the polypropylene resin compositionexhibits a substantially single melting peak as measured by adifferential scanning calorimeter.
 80. The polypropylene resincomposition as in claim 78 wherein the polypropylene polymer [A] has anisotactic triad fraction of the propylene unit chains linked head totail of 97% or more as measured by 13C-NMR.
 81. A polypropylene resinexpanded particle comprising the polypropylene resin composition asclaimed in claim 78 as a base resin.
 82. A polypropylene resin expandedparticle comprising: a core layer in an expanded state comprising thepolypropylene resin expanded particle of claim 80; and a coat layercovering the core layer wherein the coat layer comprises a thermoplasticresin.
 83. The polypropylene resin expanded particle as in claim 82,wherein the coat layer comprises an olefin polymer having a meltingpoint lower than either of the propylene polymers [A] and [B] formingthe core layer or an olefin polymer that exhibits substantially nomelting point.
 84. The polypropylene resin expanded particle as in claim82, wherein the resin composition of the core layer exhibits asubstantially single melting peak when measured using a differentialscanning calorimeter.
 85. The polypropylene resin expanded particle asin claim 82, wherein the coat layer comprises the propylene polymer [A]and/or the propylene polymer [B] of the core layer blended with anolefin polymer in the amount of 1 to 100 parts by weight of thepropylene polymer [A] and/or the propylene polymer [B] per 100 parts byweight of the olefin polymer.
 86. The polypropylene resin expandedparticle as in claim 81 wherein the polypropylene polymer [A] has anisotactic triad fraction of the propylene unit chains linked head totail of 97% or more as measured by 13C-NMR.
 87. The polypropylene resinexpanded particle as in claim 81 wherein the propylene polymer [A] has amelt flow rate of 0.5 g/10 minutes to 100 g/10 minutes.
 88. Thepolypropylene resin expanded particle as in claim 81, wherein thepolypropylene resin expanded particle further comprises a blowing agenthaving a critical temperature (Tc) represented by Formula (2):−90° C.≦Tc≦400° C.   Formula (2).
 89. A molded article produced by theprocess comprising molding the polypropylene resin expanded particlesaccording to claim 81 in a mold, wherein the molded article has adensity of 0.008 g/cm³ to 0.5 g/cm³.
 90. The molded article according toclaim 89, wherein the molded article is a shock absorber.
 91. The shockabsorber according to claim 90, wherein a density of the shock absorberis 0.02 to 0.45 g/cm³.
 92. The shock absorber according to claim 90,further comprising a skin layer disposed on a surface thereof, whereinthe skin layer has a density greater than a density of an inner portionof the shock absorber.
 93. An automobile bumper comprising the shockabsorber according to claim 90 as a core material.
 94. An automobilebumper comprising the shock absorber according to claim 91 as a corematerial.
 95. An automobile bumper comprising the shock absorberaccording to claim 92 as a core material.
 96. A molded article accordingto claim 89, comprising a crystalline structure in which a peak inherentto the base resin and a peak at higher temperature than that of theinherent peak appear as endothermic peaks on a first DSC curve obtainedwhen 2 mg to 4 mg of test specimens cut out from the molded article areheated up to 200° C. at a rate of 10° C./minute by means of adifferential scanning calorimeter.